The decade has seen significant development of relatively simple methodological approaches to relate various anthropogenic nutrient sources to their delivery to coastal waters, including watershed- and regional nutrient budgets and accounting. Advancements in our understanding of new sources, legacy sources, and spatio-temporal patterns are being achieved by using increasingly more accessible and more highly resolved data with analytical frameworks that provide a synthesis of the information to explain regional variation. One aim of such work is to improve our understanding of nutrient loading and how climate, hydrology, land use change, and other factors affect the resulting loads to coastal waters. Nutrient accounting methods, including material balances and related modelling approaches, are especially valuable for management and policy making because they relate impacts to various anthropogenic sources, and thereby facilitate development of management priorities. Presentations in this session will report on progress to date on methodologies currently in use or under development, recent applications of such approaches, and implications for environmental management and policy.
Lead Organizer: Dennis P Swaney, Cornell University (dps1@cornell.edu)
Co-organizers:
Estela Romero, Universitat Autònoma de Barcelona, CREAF (estela.romero@creaf.uab.cat)
Josette Garnier, Pierre and Marie Curie University and Sorbonne University (josette.garnier@sorbonne-universite.fr)
Presentations
05:00 PM
FATE OF ANTHROPOGENIC NITROGEN (N) AND PHOSPHORUS (P) INPUTS IN THE BALTIC SEA CATCHMENT (6669)
Primary Presenter: Bärbel Müller-Karulis, Stockholm University (barbel.muller-karulis@su.se)
Net anthropogenic N and P inputs (NANI/NAPI) to the Baltic Sea drainage basin peaked in the 1970s and 1980s and have since then stabilized on lower levels. Of the cumulative 1900 – 2018 inputs, only 15% of NANI and 6% of NAPI have left the drainage basin as waterborne loads to the Baltic Sea. To clarify the fate of the remaining inputs, we have constructed a dynamic model that routes NANI and NAPI either via rapid transfer or through mobile terrestrial and aquatic storage pools into the Baltic Sea, with losses to terrestrial and aquatic sinks in proportion to the storage pools. We have disaggregated the Baltic Sea catchment into seven regions and calibrated our model to reproduce riverine loads of N and P in each subregion. Fluxes from the mobile terrestrial storage pool dominated anthropogenic riverine N and P loads in the southern part of Baltic Sea, whereas rapid transfers were equally important in the northern boreal basins. In total, 67% of the 1900 – 2018 NANI inputs and 82% of NAPI were lost to terrestrial and aquatic sinks, and only 12% of both NANI and NAPI were still retained in mobile pools in 2018. Residence times in the mobile storage pools were 5 – 7 years for N and 10 – 22 years for P in the southern part of the Baltic Sea; but longer in the boreal basins with larger rapid losses. In 2018, mobile storage pools were close to steady-state given present inputs, but mobile P pools would continue their decline and cause a further decrease in riverine P loads.
05:15 PM
THE SEINE LAND-SEA CONTINUUM: IMPACT OF THREE AGRO-FOOD SCENARIOS ON THE QUALITY OF FRESHWATERS AND MARINE WATERS (5089)
Primary Presenter: Estela Romero, CREAF (estela.romero@creaf.uab.es)
Three future agro-food system scenarios were specified for the territory draining into the Seine Bight, comprising Paris megacity and the Seine watershed. The first scenario assumes the pursuit of the current trend of opening and specialization of agriculture, as well as of the concentration of population within the Paris agglomeration. The second scenario assesses the generalization of agroecological practices and a healthier human diet. A third hybrid scenario was elaborated assuming that agroecological practices were implemented only in some protected areas (about one-third of the total watershed area). We use a unique modelling chain (GRAFS-Riverstrahler-ECOMARS3D) that couples the biogeochemical functioning of the river basin, the estuary, and the adjacent bay. It allows consistently exploring the implications of changes in terrestrial activities throughout the aquatic continuum and assessing to what extent changes in population, agricultural practices, food consumption, and sanitation may sustain the current recovery trend or increase stress on the system. Results show that only the full agroecological scenario would restore good water quality everywhere in the river network and significantly decrease the risks of toxic algal blooms in the coastal zone. Intermediate situations, such as the protection of specific areas, however attractive as a solution, are not enough to offset the impacts of intensive human activities unless the protected areas dedicated to compensating for damage are sufficiently large.
05:30 PM
A generic land to sea modelling chain for fighting coastal eutrophication in France (5832)
Primary Presenter: Antoine Casquin, Sorbonne Université (antoine.casquin@sorbonne-universite.fr)
Water-authorities are prompt to consider coastal eutrophication in their management of water quality. Identifying admissible nutrient thresholds remains highly uncertain considering the complexity of biogeochemical processes involved in carbon and nutrient cycling that can either attenuate or exacerbate the imbalance in nutrients cascading from land to the coastal waters. A modelling chain including agricultural practices (GRAFS model), the transfer and transformations of carbon and nutrients along the hydrographic network (pyNuts-Riverstrahler model) and estuaries (C-GEM model) was designed and applied, for the first time at the scale of the entire metropolitan France, over the 2014-2019 period. Using a large database of riverine measurements (n=392,870 data from 929 stations), the results were validated for dissolved organic carbon (DOC), nitrate (NO3), dissolved phosphorus (PO4), total phosphorus (TP) and dissolved silica (DSi). This land-to-sea modelling chain allows identifying the origin of nutrient excess exported to coastal waters where it supports harmful algae blooms. Our work provides an accurate source apportionment of nutrients for 64 French sea outlets and demonstrates that efforts are still needed to reduce diffuse agricultural nutrients loads. Thanks to process-based and spatially explicit modelling tools, our approach identifies and quantifies the main processes governing the transfer of nutrients along the aquatic continuum and should ultimately sheds light on achievable levels of nutrients in marine and coastal areas.
05:45 PM
Finding control points in landscapes that influence riverine elemental loads and stoichiometry (5175)
Primary Presenter: Stéphanie Shousha, University of Montreal (stephanie.shousha@gmail.com)
Understanding how various watershed features, be they natural or anthropogenically altered, influence riverine biogeochemistry is crucial to management and maintaining aquatic ecosystem health. Net anthropogenic nitrogen and phosphorus inputs (NANI/NAPI) is a relatively simple mass balance approach that allows for the identification of concentrated areas of nutrients in watersheds as a function of human activities that has been successfully linked to predicting loadings into rivers. However, few attempts have been made to assess NANI/NAPI at scales relevant to management and evaluate how changes over time have influenced the relative importance of elemental loading. Here we present a few examples of the applicability of NANI/NAPI as a relevant tool for watershed management at the municipal scale. Furthermore, we show how historical changes and human interventions in the landscape have altered riverine loads and stoichiometries in differential ways as a function of dominant entrance pathways to provide solutions for mitigation.
06:00 PM
EFFECTS OF CLIMATE CHANGE ON NITROGEN EXPORT FROM THE PO RIVER BASIN AND EUTROPHICATION POTENTIAL IN THE ADRIATIC SEA (NORTHERN ITALY) (6312)
Primary Presenter: Elisa Soana, University of Ferrara (elisa.soana@unife.it)
Rivers worldwide are under stress from eutrophication and nitrate pollution, but the ecological consequences overlap with climate change and the resulting interactions may be complex, unexpected, and as yet unexplored. Understanding how climate change impacts on thermal and hydrological regimes may affect nutrient dynamics and transport to coastal areas is crucial for implementing effective management strategies to mitigate eutrophication in human-impacted watersheds, such as the Po River basin (northern Italy). The present work addresses the long-term trends (1992-2020) of nitrogen export to the Adriatic Sea by investigating its relationship with water temperature and discharge trajectories. Despite the constant nitrogen surplus on arable land, a marked decrease in nitrogen export, mainly as nitrate, was recorded in the last decade compared to the 1990s. The reduction of nitrogen loads in all seasons was probably related to an increased metabolic capacity of the river, triggered by warming water temperatures. An extended seasonal window of warm temperatures and the persistence of low-flow conditions are likely to stimulate denitrification and create favourable conditions for permanent nitrate removal, resulting in reduced delivery to the sea from spring to early autumn, when the risk of eutrophication is higher. The present outcomes suggest that temperature warming due to climate change would unexpectedly increase nitrogen processing efficiency, thereby reducing export from catchments and partially buffering eutrophication.
06:15 PM
CONTRIBUTION OF SUBMARINE GROUNDWATER DISCHARGES IN COASTAL NUTRIENT ENRICHMENT IN THE CILICIAN BASIN, NORTHEASTERN MEDITERRANEAN SEA (7082)
Primary Presenter: Burak Kuyumcu, Middle East Technical University (kuyumcu.h2o@gmail.com)
Anthropogenic nutrient enrichment is expected to be a significant component of the Cilician Basin nutrient budget. Quantifying submarine groundwater discharge (SGD) impacts in the basin is crucial for establishing an ecosystem-based management scheme for the region. Therefore, we aimed to quantify SGD into the basin for the first time using 228Ra mass-balance modeling approach. Two seasonal basin-scale research cruises and two seasonal expeditions were conducted in 2022. A Lagrangian particle tracking model was used to predict offshore exchange rates. Finally, we defined a box model of 228Ra budget.228Ra activities ranged between 40-174 dpm/m³ in the river and 43-257 dpm/m³ in the groundwater during the wet season. The average activities were 27.0 dpm/m³, 15.6 dpm/m³ and 7.6 dpm/m³ in the basin's surface, intermediate, and deep water, respectively. The preliminary results indicated that the annual SGD water flux might be at least equal to or even up to 44 factor larger than annual riverine fluxes into the basin. The large span in the estimations may be attributed to the lack of a saline end-member in our estimations. The groundwater 228Ra activities were lower than previously reported, which may be linked to karstic geology. A prior research from a nearby area with similar geology has shown that fresh SGD may account for 30% to 80% of total SGD. Based on this range, SGD-associated TIN, PO4, and Si fluxes might account for at least 50%, 18% and 86% of riverine nutrient loads, respectively. We conclude that SGD might be a major component of the nutrient budget of the basin.
SS028 Watershed-Based Nutrient Accounting: Biogeochemical Connections From Catchments to Coastal Waters
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Sala Menorca B