New Papers

Microplastics in the Thames

Paul Whitehead and colleagues have published a new study of microplastics in the Thames River, UK. This is an exciting paper for a number of reasons. It is one of the first realistic applications of a riverine water quality model to the problem of microplastic pollution and it is the first published paper using the INCA-Microplastics model with real data. This study also presents one of the first examples of an INCA model implemented using the open source MOBIUS framework.

Microplastic pollution of surface waters is an issue of increasing societal concern. Plastics and microplastics are ubiquitous in freshwater ecosystems. Understanding the transport and distribution of microplastics in river systems is key to assessing impacts. Modelling the main flow dynamics, mixing, sedimentation and resuspension processes is essential for an understanding of the transport processes. Professor Whitehead and colleagues applied INCA-Microplastics to the whole of the freshwater catchment of the River Thames, UK, to evaluate inputs, loads and concentrations along the river system. They calibrated the model against UK water industry measurements of microplastics in effluent discharges and sewage sludge. In their simulation, they showed significant increases in microplastic loads moving along the river system, with rising concentrations in downstream reaches and increasing deposition to the riverbed. The paper presents an assessment of potential impacts on aquatic ecosystems and a review of policy implications.

INCA-P New Papers

Modelling instream P and ecology

Jill Crossman and colleagues have just published a paper describing INCA-PEco, the Integrated Catchments model for Phosphorus Ecology. This new model is a major upgrade to the INCA-P model.

INCA-PEco integrates in-stream phosphorus (P), dissolved oxygen (DO), biological oxygen demand (BOD) and phytoplankton processes. The model simulates dissolved and particulate P transport and includes a new, more physically based streamflow submodel.

The team applied the new model to two eutrophied mesoscale catchments with differing climatic regime (continental vs. maritime) and phosphorus sources (point vs. diffuse). They used Generalised Sensitivity Analysis (GSA) to assess the effects of regional differences in climate, land use and P sources on parameter importance during calibration. In their analysis, they successfully reproduced in-stream total phosphorus (TP), suspended sediment, DO, BOD and chlorophyll-a (chl-a) concentrations across a range of temporal scales, land uses and climate regimes. While INCA-PEco is highly parameterized, they showed that model uncertainty, can be significantly reduced by focusing calibration and monitoring efforts on just 18 parameter, most of which are related to streamflow (i.e., base flow, Manning’s n and river depth). However, in catchments dominated by diffuse nutrient inputs, e.g., in agricultural areas, detailed data on crop growth and nutrient uptake rates are also important. The remaining parameters provide flexibility to the user, broaden model applicability, and maximize its functionality under a changing climate.

All model equations are exhaustively documented in the supplementary information.

New Papers

Consequences of future low flows for energy security

Giamba Bussi and Paul Whitehead published a new study of the potential consequences of drought and low flows for power generation and river ecology. Power plants often use river waters for cooling purposes and can be sensitive to droughts and low flows. Water quality is also a concern, due to algal blooms and sediment loads that might clog filters.

They coupled INCA with a climate model to assess the possible impacts of droughts on river flow and water quality and the potential consequences for power plant operation, using the River Trent (UK) as a case study. Their results suggest a significant decrease in future flows and an increase in phosphorus concentrations, potentially enhancing algal production.

These findings show that power plant operators should expect more stress in the future due to reduced cooling water availability and decreasing upstream water quality. This issue might have serious consequences for energy security.

INCA-C New Papers Uncategorized

DOC Futures in UK Uplands

Jae-young Lee and colleagues have published a novel study of possible future trends in dissolved organic carbon (DOC) concentrations in a UK upland catchment.

Over the past several several decades, rising DOC concentrations have been seen in European lakes and rivers. A number of mechanisms have been proposed to explain these trends, including climate change and recovery from acidification. Drier summers and wetter winters are projected in the UK, and this may affect DOC levels. Lee and colleagues modelled DOC in the headwaters of the River Severn. They explored the effect of changing climate and acid deposition on surface water DOC concentrations, including the “enzymatic latch” effect in peatlands during droughts. They simulated recent (1995–2013) rising trends in DOC.

They used a novel approach to simulate possible future climate. The model was run with climatic scenarios generated using the weather@home2 climate modeling platform and EMEP sulfate deposition scenarios for 1975–2100. They showed that rising DOC trends are likely to continue in the near future (2020–2049) and stabilize in the far future (2070–2099). Seasonality will also change, with a post-drought DOC surge in autumn months.

INCA-N INCA-P New Papers

Tradeoffs for agri-environmental measure effectiveness

Katri Rankinen and colleagues have published a study of the effectiveness of agri-environmental measures to reduce nitrogen (N) and phosphorus (P) loads to receiving waters in Finland.

In areas with intensive agriculture, excessive nutrient loading causes deterioration of receiving surface waters. A number of measures are used to reduce nutrient loads but there can be tradeoffs. While nitrate and particulate phosphorus load can be efficiently controlled by reducing tillage frequency and increasing vegetation cover, this often leads to increased loading of bioavailable phosphorus. In the latest phase of the EU Rural Programme, measures with the highest potential to reduce the nutrient loading to receiving waters were setting limits for fertilization of arable crops and retaining plant cover on fields with, e.g., no-till methods and uncultivated areas. Due to the latter two measures, the area of vegetation cover Finland has increased since 1995, suggesting clear effects on nutrient loading in the catchment scale as well.

In the new paper, Katri Rankinen and colleagues modeled the effectiveness of agri-environmental measures to reduce N and P loads to receiving waters. They showed that INCA-P was able to simulate both fast (immediate) and slow (non-immediate) processes that influence P loading from catchments. It was also evident that no-till methods had increased bioavailable P load to receiving waters, even though total P and total N loading were reduced.

New Papers

The Dominant Source Layer

José Ledesma’s paper on shifts in the Dominant Source Layer (DSL) under a future climate is now published in Journal of Hydrology.

The DSL is the riparian zone (RZ) depth layer that contributes most of the water and solute fluxes to streams. Specifically, the DSL concept can be used to explain timing and amount of terrestrial solutes transferred from RZs to headwater streams. Understanding the behavior of the DSL is key to predicting water quality responses to a changing climate. José and colleagues investigated the potential impact of future climate changes on the long-term position of the DSL in a subhumid Mediterranean headwater catchment. They used PERSiST to simulate reference (1981–2000) and future (2081–2100) stream runoff. Possible future conditions were simulated using synthetic temperature, precipitation, and inter-event length scenarios to project possible effects of changes in temperature, rainfall amount, and rainfall event frequency and intensity. Simulated stream runoff was then used to estimate RZ groundwater levels and DSL position. Their simulations suggested that future changes in temperature and precipitation will have similar effects on long-term DSL position. Nearly all scenarios projected drier conditions with less runoff and a deeper DSL. Shallow organic-rich layers in the RZ will likely only be hydrologically activated during sporadic, large rainfall episodes predicted for the most extreme inter-event length scenarios. In the future, terrestrial organic matter inputs to streams will decrease, likely reducing catchment organic matter exports and stream dissolved organic carbon concentrations.