Making waves: Lessons learned from the COVID-19 anthropause in the Netherlands on urban aquatic ecosystem services provisioning and management.

The anomalous past two years of the COVID-19 pandemic have been a test of human response to global crisis management as typical human activities were significantly altered. The COVID-instigated anthropause has illustrated the influence that humans and the biosphere have on each other, especially given the variety of national mobility interventions that have been implemented globally. These local COVID-19-era restrictions influenced human-ecosystem interactions through changes in accessibility of water systems and changes in ecosystem service demand. Four urban aquatic case studies in the Netherlands demonstrated shifts in human demand during the anthropause. For instance, reduced boat traffic in Amsterdam canals led to improved water clarity. In comparison, ongoing service exploitation from increased recreational fishing, use of bathing waters and national parks visitation are heightening concerns about potential ecosystem degradation. We distilled management lessons from both the case studies as well as from recent literature pertaining to ecological intactness and social relevance. Equally important to the lessons themselves, however, is the pace at which informed management practices are established after the pandemic ends, particularly as many communities currently recognize the importance of aquatic ecosystems and are amenable to their protection.

Urban hydrogeology: Transport routes and mixing of water and solutes in a groundwater influenced urban lowland catchment.

Urban areas in coastal lowlands host a significant part of the world's population. In these areas, cities have often expanded to unfavorable locations that have to be drained or where excess rain water and groundwater need to be pumped away in order to maintain dry feet for its citizens. As a result, groundwater seepage influences surface water quality in many of such urban lowland catchments. This study aims at identifying the flow routes and mixing processes that control surface water quality in the groundwater-influenced urban catchment Polder Geuzenveld, which is part of the city of Amsterdam. Geuzenveld is a highly paved urban area with a subsurface rain water collection system, a groundwater drainage system, and a main surface water system that receive runoff from pavement and roofs, shallow groundwater and direct groundwater seepage, respectively. We conducted a field survey and systematic monitoring to identify the spatial and temporal variations in water quality in runoff, ditch water, drain water, and shallow and deep groundwater. We found that Geuzenveld receives a substantial inflow of deep, O2-depleted groundwater, which is enriched in ammonium and phosphorus due to the subsurface mineralization of organic matter under sulfate-reducing conditions. This groundwater is mixed in the ditches during wet periods with O2-rich runoff, and iron- and phosphate-rich drain water. Unlike natural catchments, the newly created, separated urban flow routes lead to mixing of water in the main surface water itself, shortcutting much of the soil and shallow subsurface. This leads to low O2 and high ammonia concentrations in dry periods, which might be mitigated by water level management or artificially increasing O2 levels by water inlet or artificially aeration of the main water canals. Further research is necessary how to optimize artificial urban systems to deliver a better ecological and chemical status of the surface water.

Groundwater-surface water relations in regulated lowland catchments; hydrological and hydrochemical effects of a major change in surface water level management.

In lowland deltas with intensive land use, surface water levels are human controlled letting in river water during dry periods and discharge by pumping during wet periods. The water levels are usually maintained at a fixed level year-round or at fixed winter and (higher) summer levels. Several water authorities in The Netherlands consider implementing a more natural and flexible water level regime in nature reserves, with low levels in summer and high levels in winter. The objective of this study was to assess the catchment-scale hydrological and hydrochemical effects of such a change using water and solute balance modeling. We focus on ten study nature reserves where a conversion to flexible water management was planned or recently implemented. Monitoring data from the catchments were used for validating the water balance and as boundary condition input for the solute balance calculations. For all catchments, the results show relevant changes after implementing flexible water level management. For example, the surface water residence times increased (avg. +25%), the inlet and outlet fluxes reduced (avg. -38% and -72%), the chloride concentrations reduced (avg. -14%), and the N-tot concentrations increased (avg. +13%). Both the quantification of water flux changes and the detection of water quality risks were highly relevant for the water authorities. Customizing our approach to the specific circumstances in other low-lying artificial catchments worldwide may help local water managers in optimizing their water level management.