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Hydrochemical constituents in streams may originate from currently active sources at the surface and/or legacy sources from earlier surface inputs, waste deposits and land contamination. Distinction and quantification of these source contributions are needed for improved interpretation of tracer data and effective reduction of waterborne environmental pollutants. This article develops a methodology that recognizes and quantifies some general mechanistic differences in stream concentration and load behavior versus discharge between such source contributions. The methodology is applied to comparative analysis of stream concentration data for chloride (Cl−), copper (Cu), lead (Pb), and zinc (Zn), and corresponding data for water discharge, measured over the period 1990–2018 in multiple hydrological catchments (19 for Cl−, 11 for Cu and Zn, 10 for Pb) around the major Lake Mälaren in Sweden. For Cl−, the average load fraction of active sources is quantified to be 19%, and the average active and legacy concentration contributions as 2.9 and 11 mg/L, respectively. For the metals, the average active load fractions at outlets are 1%–3% over all catchments and 9%–14% in the relatively few catchments with mixed metal sources. Average active and legacy concentration contributions are 0.14 and 3.2 μg/L for Cu, 0.05 and 1.5 μg/L for Pb, and 1.4 and 12 μg/L for Zn, respectively. This multi-catchment analysis thus indicates a widespread prevalence of legacy sources, with greater legacy than active concentration contributions for both Cl−and the metals, and active contributions playing a greater role for chloride than for the metals. The relatively simple first-order methodology developed and applied in the study can be used to screen commonly available stream monitoring data for possible distinction of active and legacy contributions of any hydrochemical constituent in and across various hydrological catchment settings. Available at:https://onlinelibrary.wiley.com/doi/10.1002/hyp.14280

There is fragmented understanding of the interactions of environmental and socioeconomic systems, sectors and processes involved in coastal water quality evolution around the world. Environmental policies applying to the coastal environment also have either a land or a sea perspective. As such, the policies may be ill-adapted to support improvements of complex coastal environments that represent the interface of and link the land and sea systems. For instance, environmental regulations in the Baltic Sea region have not yet managed to sufficiently mitigate coastal eutrophication. To make policies relevant and effective, stakeholder perceptions of the environmental and socioeconomic interactions that determine the state of the coastal environment also need to be included in modelling for policy support. Such modelling approaches can facilitate knowledge integration and be a basis for synergistic efforts for coastal environment improvement. For such facilitation and for bridging the gap between land and sea policy perspectives on coastal environmental management, this study considers and models stakeholder-perceived environmental and socioeconomic interactions in a linked land-coast-sea system. To determine stakeholder perceptions of these interactions, multiple actors representing various inland, coastal, and marine sectors in the Swedish water management district Northern Baltic Proper have been engaged in a series of workshops to codevelop a system network diagram (SND) for the district’s land-coast-sea system. The co-developed SND is used in semi-quantitative modelling of coastal water quality behaviour under various human pressure and hydro-climatic conditions. Results show that synergistic multi-scale, transboundary and multi-actor measures are needed to improve coastal water quality, even locally. The measures also need to address the impacts of both currently active sources and legacy sources (accumulated over time from past to-present inputs) of nutrients. A fully-quantitative systems dynamics (SD) model is further developed, based on the system behaviour insights gained from the semi-quantitative interaction modelling. This is used for scenario analysis that can support policy by determining effective nutrient management pathways for meeting coastal water quality challenges under various possible socioeconomic developments along with climatic change. Nutrient contributionsto coastal waters from different sectors in the study region are then quantified considering the water and nutrient exchanges among the sectors and the natural water environments throughout the linked land-coast-sea system. Scenario outcomes are analysed based on a set of key performance indicators for the coastal environment. Such results can guide the development of effective environmental policies for coastal water quality and ecosystem management in the studied Baltic system and other coastal areas around the world. The booklet of abstracts can be found here:https://knowledge4policy.ec.europa.eu/event/2021-eu-conference-modelling-policy-support-collaborating-across-disciplines-tackle-key_en

Doctoral thesis, comprehensive summary Eutrophication endangers coastal ecosystems all over the world and is most often associated with an increase in anthropogenic nutrient loads to coastal waters, which fuel the growth of algae and create a variety of environmental problems. This is also the case for the Baltic Sea where coastal waters may be affected by various land, coast-sea, and hydroclimatic drivers and feedbacks, over different scales, including the eutrophic open sea. This thesis aims at improving our understanding of how these drivers affect coastal eutrophication and its management opportunities across the various coupled scales of the Baltic land-coast-sea system. To achieve this aim, the interactions between land-catchment, coastal, and open sea processes, and their influences on coastal eutrophication have been investigated through water quality modelling with applications to specific Baltic coastal waters. Hydroclimatic influences on the propagation of change-impacts through the land-coast-sea continuum to coastal eutrophication have also been investigated via the water quality modelling and additional analysis of actual water quality trends over the last 30 years along the Swedish coast. Moreover, coastal eutrophication research on the Baltic Sea system has been investigated through scientific literature analysis with focus on how the reported research has accounted for and linked components in the land-coast-sea system, and the aim to identify possible research gaps. Results show that impacts of water quality improvements in the open sea propagate to a large share of the coastal waters, especially for phosphorus and phytoplankton, while impacts of reducing nutrient loads from land are more localised and more pronounced for nitrogen than for phosphorus. Therefore, reducing coastal nitrogen, phosphorus and phytoplankton concentrations requires both regional measures for open sea improvements and local land-catchment measures for reduction of nutrient loads to the specific coast. Moreover, data analysis shows that trends in coastal Summer chlorophyll a (Chl-a) are well correlated with those in open sea Summer Chl-a and in riverine nitrogen loads. Regarding hydroclimatic drivers, warmer and wetter conditions are found to complicate remediation of coastal eutrophication in comparison to drier and colder conditions. In addition, trends in coastal Summer Chl-a are well correlated with those in sea-ice conditions. These results highlight the various land-based, coastal, open sea, and hydroclimatic drivers and conditions that mix, interact in and influence the coastal waters. The various driver, management, and ecosystem components involved are overall included in Baltic coastal eutrophication research. However, specific coastal management measures, and feedbacks between drivers and impacts of coastal eutrophication are under-investigated, and the social and ecological components of the whole land-coast-sea system are not well-connected in the research. Furthermore, long-lived legacy sources on land, as well as at sea, have not been much accounted for in coastal eutrophication research so far. This calls for further research on recovery time scales and specific remediation measures that can be effective against such sources, like mussel farming and wetlands. Finally, coastal eutrophication management needs to account for the influences on local coastal conditions from a melting pot of multi-scale drivers and biogeochemical as well as ecological impacts and feedbacks. Available at:http://su.diva-portal.org/smash/record.jsf?pid=diva2%3A1604157&dswid=8720