Climate change amplifies the risk of potentially toxigenic cyanobacteria.

Cyanobacterial blooms pose a significant threat to water security, with anthropogenic forcing being implicated as a key driver behind the recent upsurge and global expansion of cyanobacteria in modern times. The potential effects of land-use alterations and climate change can lead to complicated, less-predictable scenarios in cyanobacterial management, especially when forecasting cyanobacterial toxin risks. There is a growing need for further investigations into the specific stressors that stimulate cyanobacterial toxins, as well as resolving the uncertainty surrounding the historical or contemporary nature of cyanobacterial-associated risks. To address this gap, we employed a paleolimnological approach to reconstruct cyanobacterial abundance and microcystin-producing potential in temperate lakes situated along a human impact gradient. We identified breakpoints (i.e., points of abrupt change) in these time series and examined the impact of landscape and climatic properties on their occurrence. Our findings indicate that lakes subject to greater human influence exhibited an earlier onset of cyanobacterial biomass by 40 years compared to less-impacted lakes, with land-use change emerging as the dominant predictor. Moreover, microcystin-producing potential increased in both high- and low-impact lakes around the 1980s, with climate warming being the primary driver. Our findings chronicle the importance of climate change in increasing the risk of toxigenic cyanobacteria in freshwater resources.

Reconstructing historical time-series of cyanobacteria in lake sediments: Integrating technological innovation to enhance cyanobacterial management.

The global rise of cyanobacterial blooms emphasizes the need to develop tools to manage water bodies prone to cyanobacterial dominance. Reconstructing cyanobacterial baselines and identifying environmental drivers that favour cyanobacterial dominance are important to guide management decisions. Conventional techniques for estimating cyanobacteria in lake sediments require considerable resources, creating a barrier to routine reconstructions of cyanobacterial time-series. Here, we compare a relatively simple technique based on spectral inferences of cyanobacteria using visible near-infrared reflectance spectroscopy (VNIRS) with a molecular technique based on real-time PCR quantification (qPCR) of the 16S rRNA gene conserved in cyanobacteria in 30 lakes across a broad geographic gradient. We examined the sedimentary record from two perspectives: 1) relationships throughout the entire core (without radiometric dating); 2) relationships post-1900s with the aid of radiometric dating (i.e., 210Pb). Our findings suggest that the VNIRS-based cyanobacteria technique is best suited for reconstructing cyanobacterial abundance in recent decades (i.e., circa 1990 onwards). The VNIRS-based cyanobacteria technique showed agreement with those generated using qPCR, with 23 (76%) lakes showing a strong or very strong positive relationship between the results of the two techniques. However, five (17%) lakes showed negligible relationships, suggesting cyanobacteria VNIRS requires further refinement to understand where VNIRS is unsuitable. This knowledge will help scientists and lake managers select alternative cyanobacterial diagnostics where appropriate. These findings demonstrate the utility of VNIRS, in most instances, as a valuable tool for reconstructing past cyanobacterial prevalence.

Influence of climate, topography, and soil type on soil extractable phosphorus in croplands of northern glacial-derived landscapes.

Delineating the relative solubility of soil phosphorus (P) in agricultural landscapes is essential to predicting potential P mobilization in the landscape and can improve nutrient management strategies. This study describes spatial patterns of soil extractable P (easily, moderately, and poorly soluble P) in agricultural landscapes of the Red River basin and the southern Great Lakes region. Surface soils (0-30 cm) and select deeper cores (0-90 cm) were collected from 10 cropped fields ranging in terrain (near-level to hummocky), soil texture (clay to loam), composition (calcareous to noncalcareous), and climate across these differing glacial landscapes. Poorly soluble P dominated (up to 91%) total extractable P in the surface soils at eight sites. No differences in the relative solubilities of soil extractable P with microtopography were apparent in landscapes without defined surface depressions. In contrast, in landscapes with pronounced surface depressions, increased easily soluble P (Sol-P), and decreased soil P sorption capacity were found in soil in wetter, low-slope zones relative to drier upslope locations. The Sol-P pool was most important to soil P retention (up to 28%) within the surface depressions of the Red River basin and at sites with low-carbonate soils in the southern Lake Erie watershed (up to 28%), representing areas at elevated risk of soil P remobilization. This study demonstrates interrelationships among soil extractable P pools, soil development, and soil moisture regimes in agricultural glacial landscapes and provides insight into identifying potential areas for soil P remobilization and associated P availability to crops and runoff.

Phosphorus runoff from Canadian agricultural land: A dataset for 30 experimental fields.

Phosphorus (P) runoff from agricultural land plays a critical role in downstream water quality. This article summarizes P and sediment runoff data for both snowmelt and rainfall runoff from 30 arable fields in the Canadian provinces of Saskatchewan, Manitoba and Ontario. The data were collected from 216 site-years of field experiments, with climates ranging from semi-arid to humid and a wide range of field management practices. In the article, mean annual and seasonal (in terms of snowmelt and rain) precipitation inputs, runoff depths, and P and sediment concentrations and loads are presented, along with ranges of yearly values. In addition, information of field management and soil characteristics (e.g. soil type and soil Olsen P) is also presented for each field. The data have potential to be reused for national and international cross-region comparisons of P and sediment losses, constructing and validating decision-support models and tools for assessing and managing P losses in both snowmelt and rainfall runoff, and informing beneficial management practices to improve agricultural water quality. Interpretation of the data is found in "Phosphorus runoff from Canadian agricultural land: A cross-region synthesis of edge-of-field results" [1].

Determination of sediment sources in a mixed watershed within the Appalachian-St. Lawrence Lowland Regions of southern Quebec using sediment fingerprinting.

This paper identifies the main sediment sources to the Beaudet Reservoir in Quebec (Canada) using sediment fingerprinting. The reservoir, which is built on the Bulstrode River and provides drinking water to Victoriaville, has decreased in capacity by 35% in the past 35 years. This study provides new data on fingerprinting in large and complex watersheds, a first in the province of Quebec. Nine sampling sites on the Bulstrode River and its three main tributaries were selected and five sampling campaigns were conducted. Samples from river bank profiles and adjacent fields, along with suspended sediments, were collected. All samples were sieved to 2 mm and analyzed for 137Caesium, 15 geochemical elements and sieved to 63 µm for color analysis. Source classification, based on an ANOVA test to verify the independence hypothesis and iterative linear discriminant analysis to optimize the ratio of inter-group/within-group variability, resulted in four sample classes: agricultural soils, forested soils, stream bank bottom and stream bank top. A Kruskal-Wallis H test then identified 21 out of the 32 tracers with p value < 0.05. The linear discriminant analysis led to a set of 14 tracers, namely 137Cs and 13 color coefficients with a discriminating result of 94%. That combination of 137Cs and color coefficients proved to be a cost-effective fingerprint. Based on MixSIAR modeling results, this sediment fingerprinting study has demonstrated that the main sediment sources varied within the watershed but, generally, forested soil particles dominated (33 to 49%), then agricultural soils (43 to 50%) reflecting the land use changes, followed by stream bank bottoms (82%) at the Beaudet Reservoir.

Effectiveness of Vegetated Buffer Strips in Controlling Legacy Phosphorus Exports from Agricultural Land.

The continued phosphorus (P) impairment of freshwaters and the associated risk of eutrophication raise questions regarding the efficiency of current beneficial management practices (BMPs) for improving water quality. Vegetated buffer strips (VBSs) are widely encouraged BMPs for reducing P export from agricultural land. However, there is a lack of evidence regarding the long-term efficiency of VBSs for reducing legacy P losses. This research used soil analyses to investigate the P removal efficiency of an unmanaged VBS for controlling P loss from agricultural land in Manitoba, Canada, between 1954 and 2011. The results showed statistically significant retention of total P, Olsen extractable P, and 0.01 M CaCl extractable P by a 5-m wide VBS compared with field soils. We found that surface soils at 5-m into the VBS had a significantly greater P sorption capacity and a smaller degree of P saturation (DPS) than adjacent field soils. The elevated DPS in field soils is likely associated with gradual P enrichment as a result of manure or fertilizer application over time and the strong affinity of P compounds for soil. Although P stratification in the VBS over 57 yr resulted in a significant increase (∼11%) in DPS of VBS topsoil compared with VBS subsoil, our findings do not support the saturation of VBS soils with P. However, cutting and removal of vegetation from VBS could be a useful strategy to remove P from VBS and minimize possible P remobilization associated with vegetation senescence, especially where the climate is cold and runoff is dominated by snowmelt.

A deconvolutional Bayesian mixing model approach for river basin sediment source apportionment.

Increasing complexity in human-environment interactions at multiple watershed scales presents major challenges to sediment source apportionment data acquisition and analysis. Herein, we present a step-change in the application of Bayesian mixing models: Deconvolutional-MixSIAR (D-MIXSIAR) to underpin sustainable management of soil and sediment. This new mixing model approach allows users to directly account for the 'structural hierarchy' of a river basin in terms of sub-watershed distribution. It works by deconvoluting apportionment data derived for multiple nodes along the stream-river network where sources are stratified by sub-watershed. Source and mixture samples were collected from two watersheds that represented (i) a longitudinal mixed agricultural watershed in the south west of England which had a distinct upper and lower zone related to topography and (ii) a distributed mixed agricultural and forested watershed in the mid-hills of Nepal with two distinct sub-watersheds. In the former, geochemical fingerprints were based upon weathering profiles and anthropogenic soil amendments. In the latter compound-specific stable isotope markers based on soil vegetation cover were applied. Mixing model posterior distributions of proportional sediment source contributions differed when sources were pooled across the watersheds (pooled-MixSIAR) compared to those where source terms were stratified by sub-watershed and the outputs deconvoluted (D-MixSIAR). In the first example, the stratified source data and the deconvolutional approach provided greater distinction between pasture and cultivated topsoil source signatures resulting in a different posterior distribution to non-deconvolutional model (conventional approaches over-estimated the contribution of cultivated land to downstream sediment by 2 to 5 times). In the second example, the deconvolutional model elucidated a large input of sediment delivered from a small tributary resulting in differences in the reported contribution of a discrete mixed forest source. Overall D-MixSIAR model posterior distributions had lower (by ca 25-50%) uncertainty and quicker model run times. In both cases, the structured, deconvoluted output cohered more closely with field observations and local knowledge underpinning the need for closer attention to hierarchy in source and mixture terms in river basin source apportionment. Soil erosion and siltation challenge the energy-food-water-environment nexus. This new tool for source apportionment offers wider application across complex environmental systems affected by natural and human-induced change and the lessons learned are relevant to source apportionment applications in other disciplines.

Uncertainties in vegetated buffer strip function in controlling phosphorus export from agricultural land in the Canadian prairies.

Vegetated buffer strips (VBSs) are widely encouraged as a cost-effective strategy to address phosphorus (P) pollution associated with agricultural production. However, there is a lack of evidence in the effectiveness of these measures for tackling diffuse P pollution in cold-climate regions under concentrated runoff flow conditions. This research aimed to investigate the effects of VBSs on reducing P concentrations in surface runoff at three different watersheds in Manitoba, Canada. Surface runoff samples were collected in four sub-catchments from each watershed by installing paired weirs at 0.5-m and at 5-m into the VBSs along the expected runoff flow path. In addition, P concentrations were measured in soil samples collected within and outside of the runoff flow path to gain further insight into P dynamics within VBSs at each study site. The results indicate that VBSs had little or no significant effect on reducing the concentration of P forms in surface runoff in the majority of situations, resulting in reduced runoff losses of total, dissolved and particulate P concentrations in only 23, 12 and 12% of the situations, respectively. In addition, Olsen extractable P concentrations in VBS soils were not significantly different from field soils both within and outside of the flow path. The ineffective P retention by VBSs in this region is likely associated with the fact that the majority of the runoff flow is concentrated through small portions of VBSs and occurs during snowmelt when biogeochemical processes responsible for P retention in VBSs are limited. Further research is needed to develop alternative management practices that enhance P retention during concentrated snowmelt runoff events in such cold-climate regions.

Selecting Color-based Tracers and Classifying Sediment Sources in the Assessment of Sediment Dynamics Using Sediment Source Fingerprinting.

The use of sediment color as a fingerprint property to determine sediment sources is an emerging technique that can provide a rapid and inexpensive means of investigating sediment sources. The present study aims to test the feasibility of color fingerprint properties to apportion sediment sources within the South Tobacco Creek Watershed (74 km) in Manitoba, Canada. Suspended sediment from 2009 to 2011 at six monitoring stations and potential source samples along the main stem of the creek were collected. Reflectance spectra of sediments and source materials were quantified using a diffuse reflectance spectrometry, and 16 color coefficients were derived from several color space models. Canonical discriminant analysis was used to reclassify and downsize sediment source groups. After the linear additive test and stepwise discriminant function analysis, four color coefficients were chosen to fit the Stable Isotope Analysis in R model. Consistent with the conventional fingerprinting approach, the color fingerprint results demonstrated a switch in the dominant sediment source between the headwaters and the outlet of the watershed, with the main sources being topsoil in the upper reaches, whereas outcrop shale and stream bank materials dominated in the lower reaches. The color fingerprinting approach can be integrated with conventional fingerprints (e.g., geochemical and fallout radionuclide properties) to improve source discrimination, which is a key component for source ascription modeling. We concluded that the use of color fingerprints is a promising, cost-effective technique for sediment source fingerprinting.

Nutrient and sediment losses in snowmelt runoff from perennial forage and annual cropland in the canadian prairies.

An 8-yr field-scale study, 2005 to 2012, investigated effects of agricultural land use on nutrient and sediment losses during snowmelt runoff from four treatment fields in southern Manitoba. In 2005, two fields with a long-term history of annual crop (AC) production were planted to perennial forage (PF), while two other fields were left in AC production. In 2009, the AC fields were converted to PF, while the PF fields were returned to AC. Runoff flow rates were monitored at the lower edge of the fields, and nutrient concentrations of runoff water were determined. The effects of AC and PF on selected variables were similar for the spatial (between-fields) and temporal (within-field) comparisons. The flow-weighted mean concentrations (FWMCs) and loads of particulate N, P, and sediment were not affected by treatment. Soil test N and the FWMC and load of NO (NO + NO) were significantly greater in the AC treatment, but the FWMC and load of NH were greater in the PF treatment. Loads of total dissolved N (TDN) and total N (TN) were not affected by treatment, although the concentrations of TDN and TN were greater in the AC treatment. The PF treatment significantly increased FWMCs and loads of total dissolved P (TDP) and total P (TP). On an annual snowmelt runoff basis, the PF treatment increased the FWMC of TDP by 53% and TP by 52% and increased the load of TDP by 221% and TP by 160% compared with the AC treatment. The greater P and NH losses in the PF treatment were attributed mainly to nutrient release from forage residue due to freezing.

Conversion of Conservation Tillage to Rotational Tillage to Reduce Phosphorus Losses during Snowmelt Runoff in the Canadian Prairies.

In a preceding study, converting conventional tillage (ConvT) to conservation tillage (ConsT) was reported to decrease nitrogen (N) but to increase phosphorus (P) losses during snowmelt runoff. A field-scale study was conducted from 2004 to 2012 to determine if conversion of ConsT to rotational tillage (RotaT), where conservation tillage was interrupted by a fall tillage pass every other year, could effectively reduce P losses compared with ConsT. The RotaT study was conducted on long-term paired watersheds established in 1993. The ConvT field in the pair has remained under ConvT practice since 1993, whereas tillage was minimized on the ConsT field from 1997 until 2007. In fall 2007, RotaT was introduced to the ConsT field, and heavy-duty cultivator passes were conducted in the late fall of years 2007, 2009, and 2011. Runoff volume and nutrient content were monitored at the edge of the two fields, and soil and crop residue samples were taken in each field. Greater soil Olsen P and more P released from crop residue are likely the reasons for the increased P losses in the ConsT treatment (2004-2007) relative to the ConvT treatment (2004-2007). Analysis of covariance indicated that, compared with ConsT (2004-2007), RotaT (2008-2012) increased the concentrations of dissolved organic carbon (DOC) by 62%, total dissolved N (TDN) by 190%, and total N (TN) by 272% and increased the loads of DOC by 34%, TDN by 34%, and TN by 60%. However, RotaT (2008-2012) decreased soil test P in surface soil, P released from crop residue, and duration of runoff compared with ConsT (2004-2007) and thus decreased the concentrations of total dissolved P (TDP) by 46% and total P (TP) by 38% and decreased the loads of TDP by 56% and TP by 42%. In the Canadian Prairies, where P is a major environmental concern compared with N, RotaT was demonstrated to be an effective practice to reduce P losses compared with ConsT.

Critical factors affecting field-scale losses of nitrogen and phosphorus in spring snowmelt runoff in the canadian prairies.

A long-term, field-scale study in southern Manitoba, Canada, was used to identify the critical factors controlling yearly transport of nitrogen (N) and phosphorus (P) by snowmelt runoff. Flow monitoring and water sampling for total and dissolved N and P were performed at the edge of field. The flow-weighted mean concentrations and loads of N and P for the early (the first half of yearly total volume of snowmelt runoff), late (the second half of yearly total volume of snowmelt runoff), and yearly snowmelt runoff were calculated as response variables. A data set of management practices, weather variables, and hydrologic variables was generated and used as predictor variables. Partial least squares regression analysis indicated that critical factors affecting the water chemistry of snowmelt runoff depended on the water quality variable and stage of runoff. Management practices within each year, such as nitrogen application rate, number of tillage passes, and residue burial ratio, were critical factors for flow-weighted mean concentration of N, but not for P concentration or nutrient loads. However, the most important factors controlling nutrient concentrations and loads were those related to the volume of runoff, including snow water equivalent, flow rate, and runoff duration. The critical factors identified for field-scale yearly snowmelt losses provide the basis for modeling of nutrient losses in southern Manitoba and potentially throughout areas with similar climate in the northern Great Plains region, and will aid in the design of effective practices to reduce agricultural nonpoint nutrient pollution in downstream waters.

The effects of multiple beneficial management practices on hydrology and nutrient losses in a small watershed in the Canadian prairies.

Most beneficial management practices (BMPs) recommended for reducing nutrient losses from agricultural land have been established and tested in temperate and humid regions. Previous studies on the effects of these BMPs in cold-climate regions, especially at the small watershed scale, are rare. In this study, runoff and water quality were monitored from 1999 to 2008 at the outlets of two subwatersheds in the South Tobacco Creek watershed in Manitoba, Canada. Five BMPs-a holding pond below a beef cattle overwintering feedlot, riparian zone and grassed waterway management, grazing restriction, perennial forage conversion, and nutrient management-were implemented in one of these two subwatersheds beginning in 2005. We determined that >80% of the N and P in runoff at the outlets of the two subwatersheds were lost in dissolved forms, ≈ 50% during snowmelt events and ≈ 33% during rainfall events. When all snowmelt- and rainfall-induced runoff events were considered, the five BMPs collectively decreased total N (TN) and total P (TP) exports in runoff at the treatment subwatershed outlet by 41 and 38%, respectively. The corresponding reductions in flow-weighted mean concentrations (FWMCs) were 43% for TN and 32% for TP. In most cases, similar reductions in exports and FWMCs were measured for both dissolved and particulate forms of N and P, and during both rainfall and snowmelt-induced runoff events. Indirect assessment suggests that retention of nutrients in the holding pond could account for as much as 63 and 57%, respectively, of the BMP-induced reductions in TN and TP exports at the treatment subwatershed outlet. The nutrient management BMP was estimated to have reduced N and P inputs on land by 36 and 59%, respectively, in part due to the lower rates of nutrient application to fields converted from annual crop to perennial forage. Overall, even though the proportional contributions of individual BMPs were not directly measured in this study, the collective reduction of nutrient losses from the five BMPs was substantial.

Selecting and applying cesium-137 conversion models to estimate soil erosion rates in cultivated fields.

The fallout radionuclide cesium-137 ((137)Cs) has been successfully used in soil erosion studies worldwide. However, discrepancies often exist between the erosion rates estimated using various conversion models. As a result, there is often confusion in the use of the various models and in the interpretation of the data. Therefore, the objective of this study was to test the structural and parametrical uncertainties associated with four conversion models typically used in cultivated agricultural landscapes. For the structural uncertainties, the Soil Constituent Redistribution by Erosion Model (SCREM) was developed and used to simulate the redistribution of fallout (137)Cs due to tillage and water erosion along a simple two-dimensional (horizontal and vertical) transect. The SCREM-predicted (137)Cs inventories were then imported into the conversion models to estimate the erosion rates. The structural uncertainties of the conversion models were assessed based on the comparisons between the conversion-model-estimated erosion rates and the erosion rates determined or used in the SCREM. For the parametrical uncertainties, test runs were conducted by varying the values of the parameters used in the model, and the parametrical uncertainties were assessed based on the responsive changes of the estimated erosion rates. Our results suggest that: (i) the performance/accuracy of the conversion models was largely dependent on the relative contributions of water vs. tillage erosion; and (ii) the estimated erosion rates were highly sensitive to the input values of the reference (137)Cs level, particle size correction factors and tillage depth. Guidelines were proposed to aid researchers in selecting and applying the conversion models under various situations common to agricultural landscapes.

Importance of information on tillage practices in the modelling of environmental processes and in the use of environmental indicators.

Tillage has been and will always be integral to crop production. Tillage can result in the degradation of soil, water, and air quality. Of all farm management practices, tillage may have the greatest impact on the environment. A wide variety of tillage equipment, practices and systems are available to farmers, providing opportunities to enhance environmental performance. These opportunities have made tillage a popular focus of environmental policies and programs such as environmental indicators for agriculture. This paper provides a very brief examination of the role of tillage in crop production, its effect on biophysical processes and, therefore, its impact on the environment. Models of biophysical processes are briefly examined to demonstrate the importance of tillage relative to other farm management practices and to demonstrate the detail of tillage data that these models can demand. The focus of this paper is an examination of the use of information on tillage in Canada's agri-environmental indicators initiative, National Agri-environmental Health Analysis and Reporting Program (NAHARP). Information on tillage is required for several of the indicators in NAHARP. The type of data used, its source, and its quality are discussed. Recommendations regarding the collection of tillage data and use of tillage information are presented.