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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.

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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.