Stream nutrient loads at a given site are mostly derived from the catchment upstream that site. Therefore, decisions about control strategies to reduce these loads are usually taken in the context of catchment management. These include controls of point and non-point source pollutants at their source (fertiliser application, best practices, etc.) or during their transport (erosion control, riparian buffers, water treatment plants, etc.) towards the streams. Recently, there has been increasing interest in the evaluation of the relative importance of non-point sources as determinants of stream nutrient loads, although this research area is still under development due to its complexity. For instance, the relative importance of non-point sources may vary over time, and this temporal variation may depend on geologic and climatic characteristics as well as on the agricultural practices at each particular catchment. This part of the project addresses these issues in the selected scenarios (Fig. 2, see also section 3.3). From a management standpoint, this is relevant to the overall project because it is important to know which is the major source of nutrients to the stream and when there is a higher potential for nutrient export from the catchment, so that work on best practices at farms and fields can be concentrated at those times.

           Objectives of the workpackage:

1).    Estimate point and non-point sources of nitrogen and phosphorus for each of the study catchment.

2).    Relate non-point sources to catchment features (land use, topography, landscape configuration, hydrogeomorphic units distribution).

3).    Analyse seasonal variability in point and non-point sources in relation to measured in-stream loads and hydrology.

         Tasks:

To evaluate the relative importance of point and non-point sources in the selected study scenarios and to examine the relationships between land use activities in the catchment and stream nutrient loadings we will integrate data from land use/land cover with data from stream nutrient loads using a Geographic Information System (GIS). For each particular catchment, this work will be done by:

a)      Creating an inventory of point sources from wastewater treatment plants and direct industrial discharges. Most of this information will be facilitated by the water management agencies that are participants in this project.

b)      Obtaining estimates of non-point source pollution based on those catchment characteristics that are potentially related to non-point source pollution.We will also use existing non-point source pollution models (particularly MONERIS, developed by one of the leaders of this workpackage, i.e., Horst Behrendt) and calibrate them using data from our array of study catchments, since they cover a broad range of  point vs non-point source pollution situations.

c)      Mapping the catchment land cover/land use (using existing data)

d)      Describing land cover spatial configuration using landscape metrics. This description will be based on information related to catchment slope, hydrology, geomorphology, types of vegetation (either in the terrestrial ecosystem and in the riparian zones), soil type and land use. With this information we will obtain the potential nutrient export rates from each catchment.

e)      Nutrient loads from point sources and estimates of nutrient loadings from non-point sources will be compared to examine the relative importance of both sources in each particular catchment. Catchment characteristics and nutrient sources will then be related using empirical models for each particular catchment and across study catchments. These analyses will be conducted with data collected from the catchments located upstream of each study reach (see section 3.3).

To examine changes over time in the relative importance of non-point sources to stream nutrient loads, we will:

a)      Examine historical records of stream discharge and nutrient concentrations measured at locations close to the study sites.

b)      Do temporal series analyses with discharge and nutrient loads data collected at the head of each study reach (see section 3.3) during this project and at the output from point sources (i.e. sewage treatment plants).

c)      With this information we want to create a model that will provide the most predictive power with the minimum data requirements.

Processing of all the information obtained in this workpackage will allow us to examine and elucidate relationships between land-use practices and stream water “nutrient” quality as well as relationships between land-use and relative importance of non-point versus point nutrient sources.

Patterns emerging from these analyses will be included as empirical rules into the Knowledge Base of the Expert System to provide information of mechanisms controlling nutrient sources from the catchment to the stream ecosystems.

          Participants:

This part of the project will be lead by experts in this field from the University of Barcelona (Spain) and the Institute of Freshwater Ecology and Inland Fisheries (Germany). These people will set the protocol for data acquisition, co-ordinate the data processing for each catchment, and lead the across site synthesis of the data from this workpackage.