Three decades of regulation of agricultural nitrogen losses: Experiences from the Danish Agricultural Monitoring Program.

Excess nitrogen (N) losses from intensive agricultural production are a world-wide problem causing eutrophication in vulnerable aquatic ecosystems such as estuaries. Therefore, Denmark as one of the most intensively farmed countries in the world has enforced mandatory regulations on agricultural production since the late 1980s. We demonstrate the outcome of the regulations imposed on agriculture by analyzing decadal trends in nitrate (NO) concentrations and loads in streams using 29 years of detailed monitoring data and survey information on agricultural practices at field level from five intensively cultivated headwater catchments.

Nitrogen removal and greenhouse gas fluxes from integrated buffer zones treating agricultural drainage water.

Integrated buffer zones (IBZ) are novel mitigation measures designed to decrease the loading of nitrogen (N) transported by subsurface drainage systems from agricultural fields to streams. In IBZ, drainage water flows into a pond with free water surface followed by an inundated, vegetated filterbed. This design provides an environment favorable for denitrification and thus a decrease in nitrate concentration is expected as water flow through the IBZ.

Comparing nutrient reference concentrations in Nordic countries with focus on lowland rivers.

Reference conditions of water bodies are defined as the natural or minimal anthropogenically disturbed state. We compared the methods for determining total phosphorus and total nitrogen concentrations in rivers in Finland, Norway and Sweden as well as the established reference conditions and evaluated the possibility for transfer and harmonisation of methods. We found that both methods and values differed, especially for lowland rivers with a high proportion of agriculture in the catchment.

Catchment effects of a future Nordic bioeconomy: From land use to water resources.

In the future, the world is expected to rely increasingly on renewable biomass resources for food, fodder, fibre and fuel. The sustainability of this transition to bioeconomy for our water systems depends to a large extent on how we manage our land resources. Changes in land use together with climate change will affect water quantity and quality, which again will have implications for the ecosystem services provided by water resources.

Potential impacts of a future Nordic bioeconomy on surface water quality.

Nordic water bodies face multiple stressors due to human activities, generating diffuse loading and climate change. The 'green shift' towards a bio-based economy poses new demands and increased pressure on the environment. Bioeconomy-related pressures consist primarily of more intensive land management to maximise production of biomass.

Multi-functional benefits from targeted set-aside land in a Danish catchment.

In this study, we explored how a targeted land use change in a Danish catchment (River Odense) may provide multi-functional benefits through nitrogen (N)-load reductions to obtain good ecological quality in Odense estuary, protection of N-vulnerable groundwater aquifers, protection of Natura2000 sites and carbon sequestration. An N-load model linked to GIS thematic layers of known protected areas (Natura2000 sites and N-vulnerable groundwater aquifers) was utilised targeting high N-load areas to locate set-aside land. The achieved multi-functional benefits within the catchment and estuary were assessed and cost-benefit assessment was performed by dividing the total welfare costs of the set-aside by the total multi-functional benefits gained from each strategy.

Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review.

Diffusive losses of nitrogen and phosphorus from agricultural areas have detrimental effects on freshwater and marine ecosystems. Mitigation measures treating drainage water before it enters streams hold a high potential for reducing nitrogen and phosphorus losses from agricultural areas. To achieve a better understanding of the opportunities and challenges characterising current and new drainage mitigation measures in oceanic and continental climates, we reviewed the nitrate and total phosphorus removal efficiency of: (i) free water surface constructed wetlands, (ii) denitrifying bioreactors, (iii) controlled drainage, (iv) saturated buffer zones and (v) integrated buffer zones.

Controlled Drainage as a Targeted Mitigation Measure for Nitrogen and Phosphorus.

Drainage systems provide a more or less direct conduit for excess water and nutrients from fields to surface water. High nutrient loads to streams and lakes are known to adversely affect water quality and may potentially cause algae blooms. Therefore, in-field as well as edge-of-field mitigation measures that can assist in reducing the loss of nutrients are needed.

An Assessment of the Multifunctionality of Integrated Buffer Zones in Northwestern Europe.

Integrated buffer zones (IBZs) have recently been introduced in the Northwestern Europe temperate zone to improve delivery of ecosystem services compared with the services associated with long-established vegetated buffer zones. A common feature of all the studied IBZ sites is that tile drainage, which previously discharged directly into the streams, is now intercepted within the IBZ. Specifically, the design of IBZs combines a pond, where soil particles present in drain water or surface runoff can be deposited, and a planted subsurface flow infiltration zone.

Current Insights into the Effectiveness of Riparian Management, Attainment of Multiple Benefits, and Potential Technical Enhancements.

Buffer strips between land and waters are widely applied measures in diffuse pollution management, with desired outcomes across other factors. There remains a need for evidence of pollution mitigation and wider habitat and societal benefits across scales. This paper synthesizes a collection of 16 new primary studies and review papers to provide the latest insights into riparian management.

Management Options to Reduce Phosphorus Leaching from Vegetated Buffer Strips.

Vegetated buffer strips (VBS) between agricultural areas and surface waters are important retention areas for eroded particulate P through which they may obtain critically high degrees of P saturation imposing high risk of soluble P leaching. We tested topsoil removal and three harvesting frequencies (once, twice, or four times per year) of natural buffer vegetation to reduce P leaching with the aim to offset erosional P accumulation and high degrees of P saturation. We used a simple numerical time-step model to estimate changes in VBS soil P levels with and without harvest.

Nitrogen and Phosphorus Removal from Agricultural Runoff in Integrated Buffer Zones.

Integrated buffer zones (IBZs) represent a novel form of edge-of-field technology in Northwest Europe. Contrary to the common riparian buffer strips, IBZs collect tile drainage water from agricultural fields by combining a ditch-like pond (POND), where soil particles can settle, and a flow-through filter bed (FILTERBED) planted with Alnus glutinosa (L.), a European alder (black alder).

Structural and functional characteristics of buffer strip vegetation in an agricultural landscape - high potential for nutrient removal but low potential for plant biodiversity.

Vegetated buffer strips constitute a transition zone between terrestrial and aquatic ecosystems and provide several ecosystem services. Buffer strips are often applied as a mitigation measure against diffuse pollution in agricultural areas, primarily because they may retain nutrients and in this way help protect the aquatic environment. Additionally, they can improve biodiversity in an otherwise homogenous landscape and may therefore have a value in their own right.

Going with the flow: Planktonic processing of dissolved organic carbon in streams.

A large part of the organic carbon in streams is transported by pulses of terrestrial dissolved organic carbon (tDOC) during hydrological events, which is more pronounced in agricultural catchments due to their hydrological flashiness. The majority of the literature considers stationary benthic biofilms and hyporheic biofilms to dominate uptake and processing of tDOC. Here, we argue for expanding this viewpoint to planktonic bacteria, which are transported downstream together with tDOC pulses, and thus perceive them as a less variable resource relative to stationary benthic bacteria.

Documenting success stories of management of phosphorus emissions at catchment scale: an example from the pilot river Odense, Denmark.

Documentation of the effects of different mitigation measures adopted at different scales to reduce phosphorus (P) loadings to surface waters is needed to help catchment managers select the best management practices. Water quality monitoring data from the outlets of two paired catchments (the river Odense catchment versus a neighbouring control catchment) on the island of Funen, Denmark, showed significantly different trends in annual flow-weighted P concentrations during the period 2000-2013. A significant downward trend in flow-weighted particulate P (PP) concentrations (0.

Sensors in the Stream: The High-Frequency Wave of the Present.

New scientific understanding is catalyzed by novel technologies that enhance measurement precision, resolution or type, and that provide new tools to test and develop theory. Over the last 50 years, technology has transformed the hydrologic sciences by enabling direct measurements of watershed fluxes (evapotranspiration, streamflow) at time scales and spatial extents aligned with variation in physical drivers. High frequency water quality measurements, increasingly obtained by in situ water quality sensors, are extending that transformation.

Leaching of dissolved phosphorus from tile-drained agricultural areas.

We investigated leaching of dissolved phosphorus (P) from 45 tile-drains representing animal husbandry farms in all regions of Denmark. Leaching of P via tile-drains exhibits a high degree of spatial heterogeneity with a low concentration in the majority of tile-drains and few tile-drains (15% in our investigation) having high to very high concentration of dissolved P. The share of dissolved organic P (DOP) was high (up to 96%).

Successful reduction of diffuse nitrogen emissions at catchment scale: example from the pilot River Odense, Denmark.

Land-based total nitrogen (N) loadings to Danish coastal waters have been markedly reduced since 2000. This has been achieved by general measures reducing discharges from all point sources and N leaching from farmed land supplemented with more local and targeted mitigation measures such as restoration of wetlands to increase the catchment-specific N retention. In the catchment of River Odense, restoration of wetlands has been extensive.

Suspended particles only marginally reduce pyrethroid toxicity to the freshwater invertebrate Gammarus pulex (L.) during pulse exposure.

Current ecotoxicological research on particle-associated pyrethroids in freshwater systems focuses almost exclusively on sediment-exposure scenarios and sediment-dwelling macroinvertebrates. We studied how suspended particles influence acute effects of lambda-cyhalothrin and bifenthrin on the epibenthic freshwater amphipod Gammarus pulex (L.) using brief pulse exposures followed by a 144 h post exposure recovery phase.

Global effects of agriculture on fluvial dissolved organic matter.

Agricultural land covers approximately 40% of Earth's land surface and affects hydromorphological, biogeochemical and ecological characteristics of fluvial networks. In the northern temperate region, agriculture also strongly affects the amount and molecular composition of dissolved organic matter (DOM), which constitutes the main vector of carbon transport from soils to fluvial networks and to the sea, and is involved in a large variety of biogeochemical processes. Here, we provide first evidence about the wider occurrence of agricultural impacts on the concentration and composition of fluvial DOM across climate zones of the northern and southern hemispheres.

Sources, occurrence and predicted aquatic impact of legacy and contemporary pesticides in streams.

We couple current findings of pesticides in surface and groundwater to the history of pesticide usage, focusing on the potential contribution of legacy pesticides to the predicted ecotoxicological impact on benthic macroinvertebrates in headwater streams. Results suggest that groundwater, in addition to precipitation and surface runoff, is an important source of pesticides (particularly legacy herbicides) entering surface water. In addition to current-use active ingredients, legacy pesticides, metabolites and impurities are important for explaining the estimated total toxicity attributable to pesticides.

Mitigation options to reduce phosphorus losses from the agricultural sector and improve surface water quality: a review.

The EU Water Framework Directive (WFD) obliges Member States to improve the quality of surface water and groundwater. The measures implemented to date have reduced the contribution of point sources of pollution, and hence diffuse pollution from agriculture has become more important. In many catchments the water quality remains poor.

A catchment scale evaluation of multiple stressor effects in headwater streams.

Mitigation activities to improve water quality and quantity in streams as well as stream management and restoration efforts are conducted in the European Union aiming to improve the chemical, physical and ecological status of streams. Headwater streams are often characterised by impairment of hydromorphological, chemical, and ecological conditions due to multiple anthropogenic impacts. However, they are generally disregarded as water bodies for mitigation activities in the European Water Framework Directive despite their importance for supporting a higher ecological quality in higher order streams.

Integrated assessment of the impact of chemical stressors on surface water ecosystems.

The release of chemicals such as chlorinated solvents, pesticides and other xenobiotic organic compounds to streams, either from contaminated sites, accidental or direct application/release, is a significant threat to water resources. In this paper, different methods for evaluating the impacts of chemical stressors on stream ecosystems are evaluated for a stream in Denmark where the effects of major physical habitat degradation can be disregarded. The methods are: (i) the Danish Stream Fauna Index, (ii) Toxic Units (TU), (iii) SPEAR indices, (iv) Hazard Quotient (HQ) index and (v) AQUATOX, an ecological model.