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Datasets and R scripts for the COVID anthropause case study sites for the publication entitled "Lessons learned from the COVID-19 anthropause in the Netherlands on urban aquatic ecosystem services provisioning and management" When using the .csv files for Figure 2B (bathing waters, file: Zwemmen buiten) and Figure 2C (national parks; files: De Alde Feanen, De Biesbosch, De Groote Peel, Dwingelderveld, Lauwersmeer and Weerribben-Wieden), make sure the dates are in the following format: dd-mm-yyyy When running the Figure 2C codes (in R script "COVID_GoogleTrends_Script"), set the working directory to a folder containing only the national parks .csv files.

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, O 2 -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 O 2 -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 O 2 and high ammonia concentrations in dry periods, which might be mitigated by water level management or artificially increasing O 2 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.

SUMMARY: As human mobility decreased in 2020, the interaction between humans and nature changed significantly. On one hand, water clarity improved in the Amsterdam canals because boat traffic was reduced. On the other hand increased use of fishing water and national parks formed potential threats to the aquatic ecosystems. It is important to use these experiences to foster a more eco-centric mindset, building up to handling handling climate change and future pandemics. ABSTRACT: 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.

Eutrophication of water bodies has been a problem causing severe degradation of water quality in cities. To gain mechanistic understanding of the temporal dynamics of nitrogen and phosphorus in a groundwater fed low-lying urban polder, we applied high frequency monitoring in Geuzenveld, a polder in the city of Amsterdam. The high frequency monitoring equipment was installed at the pumping station where water leaves the polder. From 2016 March to 2017 June, total phosphorus (TP), ammonium (NH4), turbidity, electrical conductivity (EC), and water temperature were measured at intervals smaller than 20 minutes. This paper discusses the results at three time scales: annual scale, rain event scale, and single pumping event scale. Mixing of upwelling groundwater and runoff was the dominant hydrological process and governed the temporal pattern of the EC, while N and P fluxes from the polder were also significantly regulated by primary production and iron transformations. The mixing of groundwater and runoff water governed water quality through variation of the intensity and duration of the events. For NH4, the dominant form of N in surface water originating from groundwater seepage, we observed low concentrations during the algae growing season, while concentrations were governed by mixing of groundwater and precipitation inputs in the late autumn and winter. The depletion of dissolved NH4 in spring suggests uptake by primary producers, consistent with high chlorophyll-a, O2, and suspended solids during this period. Total P and turbidity were high during winter, due to the release of reduced iron and P from anoxic sediment to the water column. Rapid Fe2+ oxidation in the water column is the major cause of turbidity. In the other seasons, P is retained in the sediment by iron oxides. Nitrogen is exported from the polder to the downstream water bodies throughout the whole year, mostly in the form of NH4, but as organic N in spring. P leaves the polder mainly during winter, primarily associated with Fe(OH)3 colloids and as dissolved P. Based on this new understanding of the dynamics of N and P in this low lying urban catchment, it is possible to formulate management strategies that can effectively control and reduce eutrophication situation in urban polders and receiving downstream waters.

The Amsterdam area, a highly manipulated delta area formed by polders and reclaimed lakes, struggles with high nutrient levels in its surface water system. The polders receive spatially and temporally variable amounts of water and nutrients via surface runoff, groundwater seepage, sewer leakage, and via water inlets from upstream polders. Diffuse anthropogenic sources, such as manure and fertiliser use and atmospheric deposition, add to the water quality problems in the polders. The major nutrient sources and pathways have not yet been clarified due to the complex hydrological system in lowland catchments with both urban and agricultural areas. In this study, the spatial variability of the groundwater seepage impact was identified by exploiting the dense groundwater and surface water monitoring networks in Amsterdam and its surrounding polders. A total of 25 variables (concentrations of total nitrogen (TN), total phosphorus (TP), NH4, NO3, HCO3, SO4, Ca, and Cl in surface water and groundwater, N and P agricultural inputs, seepage rate, elevation, land-use, and soil type) for 144 polders were analysed statistically and interpreted in relation to sources, transport mechanisms, and pathways. The results imply that groundwater is a large source of nutrients in the greater Amsterdam mixed urban–agricultural catchments. The groundwater nutrient concentrations exceeded the surface water environmental quality standards (EQSs) in 93 % of the polders for TP and in 91 % for TN. Groundwater outflow into the polders thus adds to nutrient levels in the surface water. High correlations (R2 up to 0.88) between solutes in groundwater and surface water, together with the close similarities in their spatial patterns, confirmed the large impact of groundwater on surface water chemistry, especially in the polders that have high seepage rates. Our analysis indicates that the elevated nutrient and bicarbonate concentrations in the groundwater seepage originate from the decomposition of organic matter in subsurface sediments coupled to sulfate reduction and possibly methanogenesis. The large loads of nutrient-rich groundwater seepage into the deepest polders indirectly affect surface water quality in the surrounding area, because excess water from the deep polders is pumped out and used to supply water to the surrounding infiltrating polders in dry periods. The study shows the importance of the connection between groundwater and surface water nutrient chemistry in the greater Amsterdam area. We expect that taking account of groundwater–surface water interaction is also important in other subsiding and urbanising deltas around the world, where water is managed intensively in order to enable agricultural productivity and achieve water-sustainable cities.

In lowland deltas with intensive land use such as The Netherlands, surface water levels are tightly controlled by inlet of diverted river water during dry periods and discharge via large-scale pumping stations during wet periods. The conventional water level regime in these polder catchments is either a fixed water level year-round or an unnatural regime with a lower winter level and a higher summer level in order to optimize hydrological conditions for agricultural land use. The objective of this study was to assess the hydrological and hydrochemical effects of changing the water level management from a conventional fixed water level regime to a flexible, more natural regime with low levels in summer and high levels in winter between predefined minimum and maximum levels. Ten study catchments were hydrologically isolated and equipped with controlled inlet and outlet weirs or pumping stations. The water level management was converted into a flexible regime. We used water and solute balance modeling for catchment-scale assessments of changes in water and solute fluxes. Our model results show relevant changes in the water exchange fluxes between the polder catchment and the regional water system and between the groundwater, surface water, and field surface storage domains within the catchment. Compared to the reference water level regime, the flexible water level regime water balance scenario showed increased surface water residence times, reduced inlet and outlet fluxes, reduced groundwater-surface water exchange, and in some catchments increased overland flow. The solute balance results show a general reduction of chloride concentrations and a general increase in N-tot concentrations. The total phosphorus (P-tot) and sulfate (SO4) concentration responses varied and depended on catchment-specific characteristics. For our study catchments, our analyses provided a quantification of the water flux changes after converting towards flexible water level management. Regarding the water quality effects, this study identified the risks of increased overland flow in former agricultural fields with nutrient enriched top soils and of increased seepage of deep groundwater which can deliver extra nutrients to surface water. At a global scale, catchments in low-lying and subsiding deltas are increasingly being managed in a similar way as the Dutch polders. Applying our water and solute balance approach to these areas may prevent unexpected consequences of the implemented water level regimes.

Possible effects of climate change on ecological functioning of shallow lakes, Lake Loenderveen as a case study The European Water Framework Directive (WFD) requires all inland and coastal waters to reach "good ecological status" by 2015. The good ecological status of shallow lakes can be characterised by clear water dominated by submerged vegetation. The ecological response of shallow lakes on nutrients largely depends on morphological and hydrological features, such as water depth, retention time, water level fluctuations, bottom type, fetch etc. These features determine the "critical nutrient load" of a lake. When the actual nutrient load of a lake is higher than the critical nutrient load, the ecological quality of this lake will deteriorate, resulting in a turbid state dominated by algae. Climate change might lead to changes in both environmental factors and ecosystem response. This certainly will have an effect on the ecological status. As an illustration the results of a multidiscipline study of a shallow peaty lake (Loenderveen) are presented, including hydrology, geochemistry and ecology. Ground- and surface water flows, nutrient dynamics and ecosystem functioning have been studied culminating in an application of the ecological model of the lake (PCLake). Future scenarios were implemented through changing precipitation, evaporation and temperature. Climate change will lead to higher nutrient loads and lower critical nutrient loads. As a consequence lakes shift easier from clear water to a turbid state.