Legacy contributions to diffuse water pollution: Data-driven multi-catchment quantification for nutrients and carbon.

Legacy pollutants are increasingly proposed as possible reasons for widespread failures to improve water quality, despite the implementation of stricter regulations and mitigation measures. This study investigates this possibility, using multi-catchment data and relatively simple, yet mechanistically-based, source distinction relationships between water discharges and chemical concentrations and loads. The relationships are tested and supported by the available catchment data. They show dominant legacy contributions for total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) across catchment locations and scales, from local to country-wide around Sweden. Consistently across the study catchments, close relationships are found between the legacy concentrations of TN and TOC and the land shares of agriculture and of the sum of agriculture and forests, respectively. The legacy distinction and quantification capabilities provided by the data-driven approach of this study could guide more effective pollution mitigation and should be tested in further research for other chemicals and various sites around the world.

Distinguishing Direct Human-Driven Effects on the Global Terrestrial Water Cycle.

Population growth is increasing the pressure on water resource availability. For useful assessment and planning for societal water availability impacts, it is imperative to disentangle the direct influences of human activities in the landscape from external climate-driven influences on water flows and their variation and change. In this study we used the water balance model, a gridded global hydrological model, to quantify and distinguish human-driven change components, modified by interventions such as dams, reservoirs, and water withdrawals for irrigation, industry, and households, from climate-driven change components on four key water balance variables in the terrestrial hydrological system (evapotranspiration, runoff, soil moisture, storage change). We also analyzed emergent effect patterns in and across different parts of the world, facilitating exploration of spatial variability and regional patterns on multiple spatial scales, from pixel to global, including previously uninvestigated parts of the world. Our results show that human activities drive changes in all hydrological variables, with different magnitudes and directions depending on geographical location. The differences between model scenarios with and without human activities were largest in regions with the highest population densities. In such regions, which also have relatively large numbers of dams for irrigation, water largely tends to be removed from storage and go to feed increased runoff and evapotranspiration fluxes. Our analysis considers a more complete set of hydrological variables than previous studies and can guide further research and management planning for future hydrological and water availability trends, including in relatively data-poor parts of the world.

Gap identification in coastal eutrophication research - Scoping review for the Baltic system case.

Coastal eutrophication is a major issue worldwide, also affecting the Baltic Sea and its coastal waters. Effective management responses to coastal eutrophication require good understanding of the interacting coastal pressures from land, the open sea, and the atmosphere, and associated coastal ecosystem impacts. In this study, we investigate how research on Baltic coastal eutrophication has handled these interactions so far and what key research gaps still remain. We do this through a scoping review, identifying 832 scientific papers with a focus on Baltic coastal eutrophication. These are categorized in terms of study focus, methods, and consideration of coastal system components and land-coast-sea interactions. The coastal component categories include coastal functions (including also socio-economic driver aspects), pressures that are natural (or mediated by a natural process or system) or directly anthropogenic, and management responses. The classification results show that considerably more studies focus on coastal eutrophication pressures (52%) or impacts (39%) than on characterizing the coastal eutrophication itself (20%). Moreover, few studies investigate pressures and impacts together, indicating that feedbacks are understudied. Regarding methods, more studies focus on data collection (62%) than on linking and synthetic methods (44%; e.g., modelling), and very few studies use remote sensing (6%) or participatory (3%) methods. Coastal links with land and open sea are mentioned but much less investigated. Among the coastal functions, studies considering ecological aspects are dominant, but much fewer studies investigate human aspects and the coastal filter function. Among the coastal pressures, studies considering nutrient loads are dominant, but much fewer studies investigate the sources of these loads, especially long-lived legacy sources and possible solutions for their mitigation. Overall, few studies investigate synergies, trade-offs and incentives for various solutions to address cross-scale multi-solution management.

Soil degradation in the European Mediterranean region: Processes, status and consequences.

Soil, a non-renewable resource, sustains life on Earth by supporting around 95% of global food production and providing ecosystem services such as biomass production, filtration of contaminants and transfer of mass and energy between spheres. Unsustainable management practices and climate change are threatening the natural capital of soils, particularly in the Mediterranean region, where increasing population, rapid land-use changes, associated socio-economic activities and climate change are imposing high pressures on the region's shallow soils. Despite evidence of high soil susceptibility to degradation and desertification, the true extent of soil degradation in the region is unknown. This paper reviews and summarises the scientific literature and relevant official reports, with the aim to advance this knowledge by synthesizing, mapping, and identifying gaps regarding the status, causes, and consequences of soil degradation processes in the European Mediterranean region. This is needed as scientific underpinning of efforts to counteract soil degradation in the region. Three main degradation categories are then considered: physical (soil sealing, compaction, erosion), chemical (soil organic matter, contamination, salinisation), and biological. We find some degradation processes to be relatively well-documented (e.g. soil erosion), while others, such as loss of biodiversity, remain poorly addressed, with limited data availability. We suggest establishment of a continuous, harmonised soil monitoring system at national and regional scale in the Mediterranean region to provide comparable datasets and chart the spatial extent and temporal changes in soil degradation, and corresponding economic implications. This is critical to support decision-making and fulfilment of related sustainable development goals.

Comparative quantification of local climate regulation by green and blue urban areas in cities across Europe.

Urban growth alters environmental conditions with major consequences for climate regulation and the exposure of population to heat. Nature-based solutions may be used to alleviate the increasing urban climate pressures, but the climate regulation services that these solutions can supply for and across different urban conditions remains understudied. We comparatively investigate the urban ecosystem service realization (considering the ecosystem service supply and demand spatial interactions) of local climate regulation by vegetated (green) and water-covered (blue) areas across 660 European cities. Results show relatively robust power-law relationships with city population density (average R2 of 0.34) of main indicators of ecosystem service realization. Country-wise fitting for city-average indicators strengthens these relationships, in particular for western European cities (average R2 of 0.66). Cross-city results also show strong power-law relationship of effectiveness in ecosystem service realization with socio-economic measures like Human Development Index and GPD per capita, in particular for the area fraction of city parts with high ecosystem service realization (R2 of 0.77). The quantified relationships are useful for comparative understanding of differences in ecosystem services realization between cities and city parts, and quantitative projection of possible change trends under different types of city growth so that relevant measures can be taken to counteract undesirable trends.

Linking climate and infectious disease trends in the Northern/Arctic Region.

Recognition of climate-sensitive infectious diseases is crucial for mitigating health threats from climate change. Recent studies have reasoned about potential climate sensitivity of diseases in the Northern/Arctic Region, where climate change is particularly pronounced. By linking disease and climate data for this region, we here comprehensively quantify empirical climate-disease relationships. Results show significant relationships of borreliosis, leptospirosis, tick-borne encephalitis (TBE), Puumala virus infection, cryptosporidiosis, and Q fever with climate variables related to temperature and freshwater conditions. These data-driven results are consistent with previous reasoning-based propositions of climate-sensitive infections as increasing threats for humans, with notable exceptions for TBE and leptospirosis. For the latter, the data imply decrease with increasing temperature and precipitation experienced in, and projected for, the Northern/Arctic Region. This study provides significant data-based underpinning for simplified empirical assessments of the risks of several infectious diseases under future climate change.

Trend correlations for coastal eutrophication and its main local and whole-sea drivers - Application to the Baltic Sea.

Coastal eutrophication is a major environmental issue worldwide. In the Baltic Sea, eutrophication affects both the coastal waters and the open sea. Various policy frameworks aim to hinder its progress but eutrophication-relevant water quality variables, such as chlorophyll-a concentrations, still exhibit opposite temporal trends in various Baltic Sea marine and coastal waters. In this study, we investigate the temporal-trend linkages of measured water quality variables and their various anthropogenic, climatic and hydrospheric drivers over the period 1990-2020 with focus on the Swedish coastal waters and related marine basins in the Baltic Sea. We find that it is necessary to distinguish more and less isolated coastal waters, based on their water exchanges with the open sea, to capture different coastal eutrophication dynamics. In less isolated coastal waters, eutrophication is primarily related to nitrogen concentrations, while it is more related to phosphorus concentrations in more isolated coastal waters. In the open sea, trends in eutrophication conditions correlate best with trends in climatic and hydrospheric drivers, like wind speed and water salinity, respectively. In the coastal waters, driver signals are more mixed, with considerable influences from anthropogenic land-based nutrient loads and sea-ice cover duration. Summer chlorophyll-a concentration in the open sea stands out as a main change driver of summer chlorophyll-a concentration in less isolated coastal waters. Overall, coastal waters are a melting pot of driver influences over various scales, from local land-based drivers to large-scale total catchment and open sea conditions. The latter in turn depend on long-term integration of pathway-dependent influences from the various coastal parts of the Baltic Sea and their land-based nutrient load drivers, combined with overarching climate conditions and internal feedback loops. As such, our results challenge any unidirectional local source-to-sea paradigm and emphasize a need for concerted local land-catchment and whole-sea measures for robust coastal eutrophication management.

Scientists' warning to humanity on the freshwater biodiversity crisis.

Freshwater ecosystems provide irreplaceable services for both nature and society. The quality and quantity of freshwater affect biogeochemical processes and ecological dynamics that determine biodiversity, ecosystem productivity, and human health and welfare at local, regional and global scales. Freshwater ecosystems and their associated riparian habitats are amongst the most biologically diverse on Earth, and have inestimable economic, health, cultural, scientific and educational values. Yet human impacts to lakes, rivers, streams, wetlands and groundwater are dramatically reducing biodiversity and robbing critical natural resources and services from current and future generations. Freshwater biodiversity is declining rapidly on every continent and in every major river basin on Earth, and this degradation is occurring more rapidly than in terrestrial ecosystems. Currently, about one third of all global freshwater discharges pass through human agricultural, industrial or urban infrastructure. About one fifth of the Earth's arable land is now already equipped for irrigation, including all the most productive lands, and this proportion is projected to surpass one third by midcentury to feed the rapidly expanding populations of humans and commensal species, especially poultry and ruminant livestock. Less than one fifth of the world's preindustrial freshwater wetlands remain, and this proportion is projected to decline to under one tenth by midcentury, with imminent threats from water transfer megaprojects in Brazil and India, and coastal wetland drainage megaprojects in China. The Living Planet Index for freshwater vertebrate populations has declined to just one third that of 1970, and is projected to sink below one fifth by midcentury. A linear model of global economic expansion yields the chilling prediction that human utilization of critical freshwater resources will approach one half of the Earth's total capacity by midcentury. Although the magnitude and growth of the human freshwater footprint are greater than is generally understood by policy makers, the news media, or the general public, slowing and reversing dramatic losses of freshwater species and ecosystems is still possible. We recommend a set of urgent policy actions that promote clean water, conserve watershed services, and restore freshwater ecosystems and their vital services. Effective management of freshwater resources and ecosystems must be ranked amongst humanity's highest priorities.

Implications of Projected Hydroclimatic Change for Tularemia Outbreaks in High-Risk Areas across Sweden.

Hydroclimatic change may affect the range of some infectious diseases, including tularemia. Previous studies have investigated associations between tularemia incidence and climate variables, with some also establishing quantitative statistical disease models based on historical data, but studies considering future climate projections are scarce. This study has used and combined hydro-climatic projection outputs from multiple global climate models (GCMs) in phase six of the Coupled Model Intercomparison Project (CMIP6), and site-specific, parameterized statistical tularemia models, which all imply some type of power-law scaling with preceding-year tularemia cases, to assess possible future trends in disease outbreaks for six counties across Sweden, known to include tularemia high-risk areas. Three radiative forcing (emissions) scenarios are considered for climate change projection until year 2100, incuding low (2.6 Wm-2), medium (4.5 Wm-2), and high (8.5 Wm-2) forcing. The results show highly divergent changes in future disease outbreaks among Swedish counties, depending primarily on site-specific type of the best-fit disease power-law scaling characteristics of (mostly positive, in one case negative) sub- or super-linearity. Results also show that scenarios of steeper future climate warming do not necessarily lead to steeper increase of future disease outbreaks. Along a latitudinal gradient, the likely most realistic medium climate forcing scenario indicates future disease decreases (intermittent or overall) for the relatively southern Swedish counties Örebro and Gävleborg (Ockelbo), respectively, and disease increases of considerable or high degree for the intermediate (Dalarna, Gävleborg (Ljusdal)) and more northern (Jämtland, Norrbotten; along with the more southern Värmland exception) counties, respectively.

Variability and change in the hydro-climate and water resources of Iran over a recent 30-year period.

Comprehensive assessment of hydro-climatic variations and change trends is essential for understanding, mitigating, and adapting to key water resource changes in different parts of the world. We performed such an assessment on Iran, as representative of an arid/semi-arid and geopolitically important world region. We acquired and calculated data time series of surface temperature (T), precipitation (P), runoff (R), evapotranspiration (ET), and water storage change (DS), to determine their status and changes in and among the 30 main hydrological basins in Iran over the period 1986-2016. From 1986-2000 to 2001-2016, the country warmed, P mostly decreased and R even more so, while water storage was depleted (DS < 0) and ET increased in some basins. Overall, the extra water provided from primarily groundwater depletion has fed and kept ET at levels beyond those sustained by the annually renewable water input from P. This indicates unsustainable use of water for maintaining and expanding human activities, such as irrigated agriculture, in this part of the world.

Close co-variation between soil moisture and runoff emerging from multi-catchment data across Europe.

Soil moisture is an important variable for land-climate and hydrological interactions. To investigate emergent large-scale, long-term interactions between soil moisture and other key hydro-climatic variables (precipitation, actual evapotranspiration, runoff, temperature), we analyze monthly values and anomalies of these variables in 1378 hydrological catchments across Europe over the period 1980-2010. The study distinguishes results for the main European climate regions, and tests how sensitive or robust they are to the use of three alternative observational and re-analysis datasets. Robustly across the European climates and datasets, monthly soil moisture anomalies correlate well with runoff anomalies, and extreme soil moisture and runoff values also largely co-occur. For precipitation, evapotranspiration, and temperature, anomaly correlation and extreme value co-occurrence with soil moisture are overall lower than for runoff. The runoff results indicate a possible new approach to assessing variability and change of large-scale soil moisture conditions by use of long-term time series of monitored catchment-integrating stream discharges.

Wetlandscape size thresholds for ecosystem service delivery: Evidence from the Norrström drainage basin, Sweden.

Wetlands are interconnected with the larger surrounding landscape through the hydrological cycling of water and waterborne substances. Therefore, the borders of individual wetlands may not be appropriate landscape system boundaries for understanding large-scale functions and ecosystem services of wetlandscapes (wetland network - landscape systems), and how these can be impacted by climate and land-use changes. Recognizing that such large-scale behaviours may not be easily predicted by simple extrapolation of individual wetland behaviours, we here investigate properties of 15 Swedish wetlandscapes in the extensive (22 650 km2) Norrström drainage basin (NDB) comprising as many as 1699 wetlands. Results based on wetland survey data in combination with GIS-based ecohydrological analyses showed that wetlands located in wetlandscapes above a certain size (in the NDB: ~250 km2) consistently formed networks with characteristics required to support key ecosystem services such as nutrient/pollutant retention and biodiversity support. This was in contrast to smaller wetlandscapes (<250 km2), which had smaller and less diverse wetlands with insufficient throughflow to significantly impact large-scale flows of water and nutrients/pollutants. The existence of such wetlandscape-size thresholds is consistent with scale-dependent flow accumulation patterns in catchments, suggesting likely transferability of this result also to other regions.

Understanding interactions between urban development policies and GHG emissions: A case study in Stockholm Region.

Human-induced urban growth and sprawl have implications for greenhouse gas (GHG) emissions that may not be included in conventional GHG accounting methods. Improved understanding of this issue requires use of interactive, spatial-explicit social-ecological systems modeling. This paper develops a comprehensive approach to modeling GHG emissions from urban developments, considering Stockholm County, Sweden as a case study. GHG projections to 2040 with a social-ecological system model yield overall greater emissions than simple extrapolations in official climate action planning. The most pronounced difference in emissions (39% higher) from energy use single-residence buildings resulting from urban sprawl. And this difference is not accounted for in the simple extrapolations. Scenario results indicate that a zoning policy, restricting urban development in certain areas, can mitigate 72% of the total emission effects of the model-projected urban sprawl. The study outcomes include a decision support interface for communicating results and policy implications with policymakers.

Potential for Hydroclimatically Driven Shifts in Infectious Disease Outbreaks: The Case of Tularemia in High-Latitude Regions.

Hydroclimatic changes may be particularly pronounced in high-latitude regions and can influence infectious diseases, jeopardizing regional human and animal health. In this study, we consider the example of tularemia, one of the most studied diseases in high-latitude regions, which is likely to be impacted by large regional hydroclimatic changes. For this disease case, we use a validated statistical model and develop a method for quantifying possible hydroclimatically driven shifts in outbreak conditions. The results show high sensitivity of tularemia outbreaks to certain combinations of hydroclimatic variable values. These values are within the range of past regional observations and may represent just mildly shifted conditions from current hydroclimatic averages. The methodology developed also facilitates relatively simple identification of possible critical hydroclimatic thresholds, beyond which unacceptable endemic disease levels may be reached. These results call for further research on how projected hydroclimatic changes may affect future outbreaks of tularemia and other infectious diseases in high-latitude and other world regions, with particular focus on critical thresholds to high-risk conditions. More research is also needed on the generality and spatiotemporal transferability of statistical disease models.

Meeting sustainable development challenges in growing cities: Coupled social-ecological systems modeling of land use and water changes.

Ongoing urban expansion may degrade natural resources, ecosystems, and the services they provide to human societies, e.g., through land use and water changes and feedbacks. In order to control and minimize such negative impacts of urbanization, best practices for sustainable urban development must be identified, supported, and reinforced. To accomplish this, assessment methods and tools need to consider the couplings and feedbacks between social and ecological systems, as the basis for improving the planning and management of urban development. Collaborative efforts by academics, urban planners, and other relevant actors are also essential in this context. This will require relevant methods and tools for testing and projecting scenarios of coupled social-ecological system (CSES) behavior, changes, and feedbacks, in support of sustainable development of growing cities. This paper presents a CSES modeling approach that can provide such support, by coupling socio-economically driven land use changes and associated hydrological changes. The paper exemplifies and tests the applicability of this approach for a concrete case study with relevant data availability, the Tyresån catchment in Stockholm County, Sweden. Results show that model integration in the approach can reveal impacts of urbanization on hydrological and water resource, and the implications and feedbacks for urban societies and ecosystems. The CSES approach introduces new model challenges, but holds promise for improved model support towards sustainable urban development.

Assessing flood probability for transportation infrastructure based on catchment characteristics, sediment connectivity and remotely sensed soil moisture.

Flooding may damage important transportation infrastructures, such as roads, railways and bridges, which need to be well planned and designed to be able to withstand current and possible future climate-driven increases in flood frequencies and magnitudes. This study develops a novel approach to predictive statistical modelling of the probability of flooding at major road-stream intersection sites, where water, sediment and debris can accumulate and cause failure of drainage facilities and associated road damages. Two areas in south-west Sweden, affected by severe floods in August 2014, are used in representative case studies for this development. A set of physical catchment-descriptors (PCDs), characterizing key aspects of topography, morphology, soil type, land use, hydrology (precipitation and soil moisture) and sediment connectivity in the water- and sediment-contributing catchments, are used for the predictive flood modelling. A main novel contribution to such modelling is to integrate the spatiotemporal characteristics of remotely-sensed soil moisture in indices of sediment connectivity (IC), thereby also allowing for investigation of the role of soil moisture in the flood probability for different road-stream intersections. The results suggest five categories of PCDs as especially important for flood probability quantification and identification of particularly flood-prone intersections along roads (railways, etc.) These include: channel slope at the road-stream intersection and average elevation, soil properties (mainly percentage of till), land use cover (mainly percentage of urban areas), and a sediment connectivity index that considers soil moisture in addition to morphology over the catchment.

Drought reduces blue-water fluxes more strongly than green-water fluxes in Europe.

Drought comprehensively affects different interlinked aspects of the terrestrial water cycle, which have so far been mostly investigated without direct comparison. Resolving the partitioning of water deficit during drought into blue-water runoff and green-water evapotranspiration fluxes is critical, as anomalies in these fluxes threaten different associated societal sectors and ecosystems. Here, we analyze the propagation of drought-inducing precipitation deficits through soil moisture reductions to their impacts on blue and green-water fluxes by use of comprehensive multi-decadal data from > 400 near-natural catchments along a steep climate gradient across Europe. We show that soil-moisture drought reduces runoff stronger and faster than it reduces evapotranspiration over the entire continent. While runoff responds within weeks, evapotranspiration can be unaffected for months. Understanding these drought-impact pathways across blue and green-water fluxes and geospheres is essential for ensuring food and water security, and developing early-warning and adaptation systems in support of society and ecosystems.

Data-driven analysis of nutrient inputs and transfers through nested catchments.

A data-driven screening methodology is developed for estimating nutrient input and retention-delivery in catchments with measured water discharges and nutrient concentrations along the river network. The methodology is applied to the Sava River Catchment (SRC), a major transboundary catchment in southeast Europe, with seven monitoring stations along the main river, defining seven nested catchments and seven incremental subcatchments that are analysed and compared in this study. For the relatively large nested catchments (>40,000km2), characteristic regional values emerge for nutrient input per unit area of around 30T/yr/km2 for dissolved inorganic nitrogen (DIN) and 2T/yr/km2 for total phosphorus (TP). For the smaller nested catchments and incremental subcatchments, corresponding values fluctuate and indicate hotspot areas with total nutrient inputs of 158T/yr/km2 for DIN and 13T/yr/km2 for TP. The delivered fraction of total nutrient input mass (termed delivery factor) and associated nutrient loads per area are scale-dependent, exhibiting power-law decay with increasing catchment area, with exponents of around 0.2-0.3 for DIN and 0.3-0.5 for TP. For the largest of the nested catchments in the SRC, the delivery factor is around 0.08 for DIN and 0.03 for TP. Overall, the nutrient data for nested catchments within the SRC show consistency with previously reported data for multiple nested catchments within the Baltic Sea Drainage Basin, identifying close nutrient relationships to driving hydro-climatic conditions (runoff for nutrient loads) and socio-economic conditions (population density and farmland share for nutrient concentrations).

Distinction, quantification and mapping of potential and realized supply-demand of flow-dependent ecosystem services.

This study addresses and conceptualizes the possible dependence of ecosystem services on prevailing air and/or water flow processes and conditions, and particularly on the trajectories and associated spatial reach of these flows in carrying services from supply to demand areas in the landscape. The present conceptualization considers and accounts for such flow-dependence in terms of potential and actually realized service supply and demand, which may generally differ and must therefore be distinguished due to and accounting for the prevailing conditions of service carrier flows. We here concretize and quantify such flow-dependence for a specific landscape case (the Stockholm region, Sweden) and for two examples of regulating ecosystem services: local climate regulation and storm water regulation. For these service and landscape examples, we identify, quantify and map key areas of potential and realized service supply and demand, based for the former (potential) on prevailing relatively static types of landscape conditions (such as land-cover/use, soil type and demographics), and for the latter (realized) on relevant carrier air and water flows. These first-order quantification examples constitute first steps towards further development of generally needed such flow-dependence assessments for various types of ecosystem services in different landscapes over the world.

Optimal Wastewater Loading under Conflicting Goals and Technology Limitations in a Riverine System.

This paper investigates a novel simulation-optimization (S-O) framework for identifying optimal treatment levels and treatment processes for multiple wastewater dischargers to rivers. A commonly used water quality simulation model, Qual2K, was linked to a Genetic Algorithm optimization model for exploration of relevant fuzzy objective-function formulations for addressing imprecision and conflicting goals of pollution control agencies and various dischargers. Results showed a dynamic flow dependence of optimal wastewater loading with good convergence to near global optimum. Explicit considerations of real-world technological limitations, which were developed here in a new S-O framework, led to better compromise solutions between conflicting goals than those identified within traditional S-O frameworks. The newly developed framework, in addition to being more technologically realistic, is also less complicated and converges on solutions more rapidly than traditional frameworks. This technique marks a significant step forward for development of holistic, riverscape-based approaches that balance the conflicting needs of the stakeholders.