Sven Teurlincx

The presence of submerged macrophytes is a desired environmental target for coastal freshwater ecosystems. Maintaining a rich community of these species can be challenging as salinisation by sea-level rise poses an increasing threat to ecosystem integrity. We tested the effect of salinisation on the growth and germination of freshwater macrophytes experimentally using field sediment. In a 56-day experiment, a macrophyte community was exposed to salinity treatments representing seasonal water management scenarios (a decreasing salinity from 1,500 to 300 mg NaCl/L, a stable salinity of 300 mg NaCl/L, an increasing salinity from 300 to 1,500 mg NaCl/L and a stable salinity of 1,500 mg NaCl/L), crossed with treatments simulating periodic turbidity pulses. All species except Elodea nuttallii grew poorly on the saline and eutrophic sediment, reflecting the challenges of growth in eutrophic coastal systems. Surprisingly, the highest community biomass was achieved in the salinity scenario of 1,500 mg NaCl/L. In a second experiment, field-collected sediments were incubated at 300 and 1,500 mg NaCl/L salinity (representing summer and winter scenarios), and the germination capacity of the existing seedbank was quantified. Most germinated seedlings did not reach maturity irrespective of salinity treatment. This indicated that sediment salinity, rather than water column salinity, determined seedling establishment success. Interestingly, the established species were characteristic of freshwater habitats, thus indicating maladaptation of the seedbank. Our results show that a mismatch between the high salinity level of eutrophic sediment and the overlaying freshwater may hamper macrophyte growth. Furthermore, target species in coastal eutrophic freshwaters should be evaluated carefully. Elodea nuttalli, which has a wide tolerance range for nutrients and salinity, outperformed other macrophyte species in our study. Thus, species with similar traits may be most successful in establishing macrophyte stands in coastal eutropic wetlands.

Ecological thresholds are useful indicators for water quality managers to define limits to nutrient pollution. A common approach to estimating ecological thresholds is using critical nutrient loads. Critical nutrient loads are typically defined as the loads at which the phytoplankton chlorophyll-a exceeds a certain concentration. However, national policies, such as in China, use chemical indicators (nitrogen and phosphorus concentrations) rather than ecological indicators (phytoplankton chlorophyll-a) to assess water quality. In this study, we uniquely define the critical nutrient loads based on maximum allowable nutrient concentrations for lake Baiyangdian. We assess whether current and future nutrient loads in this lake comply with the Chinese Water Quality standards. To this end, we link two models (MARINA-Lakes and PCLake+). The PCLake+ model was applied to estimate the critical nutrient loads related to ecological thresholds for total nitrogen, total phosphorus and chlorophyll-a. The current (i.e., 2012) and future (i.e., 2050) nutrient loads were derived from the water quality MARINA-Lakes model. Nitrogen loads exceeded the nitrogen threshold in 2012. Phosphorus loads were below all ecological thresholds in 2012. Ecological thresholds are exceeded in 2050 with limited environmental policies, and urbanization may increase nutrient loads above the ecological thresholds in 2050. Recycling and reallocating animal manure is needed to avoid future water pollution in Lake Baiyangdian. Our study highlights the need for effective policies for clean water based on policy-relevant indicators.

Water quality improvement to avoid excessive phytoplankton blooms often requires eutrophication management where both phosphorus (P) and nitrogen (N) play a role. While empirical eutrophication studies and ecological resource competition theory both provide insight into phytoplankton abundance in response to nutrient loading, they are not seamlessly linked in the current state of eutrophication research. We argue that understanding species competition for multiple nutrients and light in natural phytoplankton communities is key to assessing phytoplankton abundance under changing nutrient supply. Here we present GPLake-S, a mechanistic model rooted in ecological resource competition theory, which has only eight parameters and can predict chlorophyll-a to nutrient relationships for phytoplankton communities under N, P, N+P colimitation and light limitation. GPLake-S offers a simple mechanistic tool to make first estimates of chlorophyll-a levels and nutrient thresholds for generic lake properties, accounting for variation in N:P ratio preferences of phytoplankton species. This makes the model supportive of water management and policy.

Globally the number of relatively deep, isolated lakes is increasing because of sand, gravel, or clay excavation activities. The major excavation areas are located within the delta of rivers, and thus the deep freshwater ecosystems formed upon excavation, called quarry lakes, are unique to the landscape. They are embedded in a landscape comprised of shallow, naturally formed lakes. Given that quarry lakes are by definition novel ecosystems, water managers face difficulties in optimally managing them to deliver ecosystem services using existing frameworks designed for natural ecosystems. All lakes in delta areas are subject to similar pressures such as urbanization and eutrophication, leading to shifts in biodiversity and ecosystem functioning, and ultimately changing the ecosystem services the systems can provide. We propose a framework to enable water managers to assess the provision of ecosystem services by quarry lakes based on their ecological quality. For each ecosystem service we determined threshold values of ecological quality based on available scientific literature, an extensive field survey of 51 quarry lakes in the Netherlands, or expert knowledge. To illustrate the usefulness of our approach, we applied our framework to a lake before and after a rehabilitation focused on improving the nutrient status of the waterbody. Assessing ecosystem services under varying levels of ecological health is important to initiate action from legislators, managers, and communities.

Parasites are generally considered the most commonly occurring type of consumers, yet their biomass and population dynamics are rarely quantified at community level. Here, we used 12 years of weekly or fortnightly monitoring data (518 time points) to determine the occurrence of chytrids, fungal parasites of phytoplankton, to assess their seasonality and long-term (seasonally-detrended) dynamics in the pelagic plankton community of a temperate, eutrophic, and polymictic lake. Chytrid infections were observed in c. 75% of all samples with recurrent infections in multiple host taxa. Infection prevalence was highest in spring, but infections occurred throughout the entire year with an average of 2.3 host taxa infected per time point (ranging from 0 to 10 host taxa) and an average infection prevalence of 2.78% (ranging from 0% to 47.35%). Infected host biomass equalled that of the carnivorous zooplankton and decreased over time, while infection prevalence remained unchanged. Seasonal infection prevalence increased with phytoplankton biomass, but decreased with increasing temperature and phosphorus concentrations, reflecting that peak prevalence occurred in spring when temperature and phosphorus concentrations were relatively low. In contrast, seasonally-detrended prevalence increased with temperature, but decreased with increasing phosphorus concentrations. Chytrids are a common component of the pelagic plankton community with sizeable biomass and removing an—at times—substantial proportion of the primary production, challenging the long-standing underrepresentation of parasites in ecological studies. Chytrids responded differentially to seasonal variation and long-term trends in host density, water temperature and nutrient availability, highlighting the need to disentangle seasonal signals from long-term changes.

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.

Progressively more community initiatives have been undertaken over last decades to monitor water quality. Biological data collected by volunteers has been used for biodiversity and water quality studies. Despite the many citizen science projects collecting and using macroinvertebrates, the number of scientific peer-reviewed publications that use this data, remains limited. In 2018, a citizen science project on biological water quality assessment was launched in the Netherlands. In this project, volunteers collect macroinvertebrates from a nearby waterbody, identify and count the number of specimens, and register the catch through a web portal to instantaneously receive a water quality score based on their data. Water quality monitoring in the Netherlands is traditionally the field of professionals working at water authorities. Here, we compare the data from the citizen science project with the data gathered by professionals. We evaluate information regarding type and distribution of sampled waterbodies and sampling period, and compare general patterns in both datasets with respect to collected animals and calculated water quality scores. The results show that volunteers and professionals seldomly sample the same waterbody, that there is some overlap in sampling period, and that volunteers more frequently sampled urban waters and smaller waterbodies. The citizen science project is thus yielding data about understudied waters and this spatial and temporal complementarity is useful. The character and thoroughness of the assessments by volunteers and professionals are likely to differentiate. Volunteers collected significantly lower numbers of animals per sample and fewer animals from soft sediments like worms and more mobile individuals from the open water column such as boatsmen and beetles. Due to the lack of simultaneous observations at various locations by volunteers and professionals, a direct comparison of water quality scores is impossible. However, the obtained patterns from both datasets show that the water quality scores between volunteers and professionals are dissimilar for the different water types. To bridge these differences, new tools and processes need to be further developed to increase the value of monitoring biological water quality by volunteers for professionals.