Design of best management practice applications for diffuse phosphorus pollution using interactive GIS

Particulate PhozzyLogic Index for policy makers-an index for a more accurate and transparent identification of critical source areas

The identification of critical source areas (CSAs) is a key element in a cost-effective mitigation of diffuse emissions of phosphorus from agricultural soils into surface waters. One of the challenges related to CSAs is how to couple complex, data-intensive fate and transport models with easy-to-use information on field level for management purposes at the scale of large watersheds. To fill such a gap and create a bridge between the two tasks, this study puts forward the new Particulate PhozzyLogic Index (PPLI) based on the innovative combination of the results of a complex watershed model (in this case the PhosFate model) with fuzzy logic. Its main feature is the ability to transform the results of diverse scenarios or even models into a final map showing a catchment-wide ranking of the possibility of high PP emissions reaching surface waters for all agricultural fields. Further, this study enhances the PhosFate model with a new algorithm for the allocation of particulate phosphorus (PP) loads entering surface waters to their sources of origin. This is a basic requirement for the identification of critical PP source areas and in consequence for a cost-effective implementation of mitigation measures. By means of a sensitivity analysis, this study investigates the impacts of storm drains, discharge frequencies and flow directions on the designation of CSAs with the help of present-day scenarios for a case study catchment with an area of several hundred square kilometres. The upfront model calibration exhibits a Nash-Sutcliffe efficiency (NSE) of about 0.95 and a modified Nash-Sutcliffe efficiency (mNSE) of around 0.83. A core result of the sensitivity analysis is that the scenarios at least partially disagree on the identified CSAs and suggest that especially open furrows at field borders have the potential to lead to deviating outcomes. All scenario results nevertheless support the 80:20 rule, which states that about 80% of the phosphorus inputs into the surface waters of a catchment originate from only about 20% of its area.

Lessons Learnt from the Long-Term Management of a Large (Re)constructed Wetland, the Kis-Balaton Protection System (Hungary)

Environmental management decisions should be made based on solid scientific evidence that relies on monitoring and modeling. In practice, changing economic, societal, and political boundary conditions often interfere with management during large, long, and complex projects. The result may be a sub-optimal development path that may finally diverge from the original intentions and be economically or technically ineffective. Nevertheless, unforeseen benefits may be created in the end. The Kis-Balaton wetland system is a typical illustration of such a case. Despite tremendous investments and huge efforts put in monitoring and modeling, the sequence of decisions during implementation can hardly be considered optimal. We use a catchment model and a basic water quality model to coherently review the impacts of management decisions during the 30-year history. Due to the complexity of the system, science mostly excelled in finding explanations for observed changes after the event instead of predicting the impacts of management measures a priori. In parallel, the political setting and sectoral authorities experienced rearrangements during system implementation. Despite being expensive as a water quality management investment originally targeting nutrient removal, the Kis-Balaton wetland system created a huge ecological asset, and thereby became worth the price.

Assessing the Impact of Storm Drains at Road Embankments on Diffuse Particulate Phosphorus Emissions in Agricultural Catchments

This study presents a simple mapping key suitable for quick and systematic assessments of the types of agricultural and civil engineering structures present in a certain agricultural catchment as well as the impact they may have on the spatial distribution of critical source areas. An application of this mapping key to three small sub-catchments of a case study catchment with an area of several hundred square kilometres (one-stage cluster sampling) in Austria clearly reveals that road embankments with subsurface drainage can exert a major influence on emissions and transport pathways of sediment-bound pollutants like particulate phosphorus (PP). Due to this, the semi-empirical, spatially distributed PhosFate model is extended to separately model PP emissions into surface waters via storm drains along road embankments. Furthermore, the overall share of road embankments with subsurface drainage on all road embankments in the case study catchment is inferred with the help of a Bayesian hierarchical model. The combination of the results of these two models shows that the share of storm drains at road embankments on total PP emissions ranges from about one fifth to one third in the investigated area.

Identification of phosphorus emission hotspots in agricultural catchments

An enhanced transport-based management approach is presented, which is able to support cost-effective water quality management with respect to diffuse phosphorus pollution. Suspended solids and particulate phosphorus emissions and their transport were modeled in two hilly agricultural watersheds (Wulka River in Austria and Zala River in Hungary) with an improved version of the catchment-scale PhosFate model. Source and transmission areas were ranked by an optimization method in order to provide a priority list of the areas of economically efficient (optimal) management alternatives. The model was calibrated and validated at different gauges and for various years. The spatial distribution of the emissions shows that approximately one third of the catchment area is responsible for the majority of the emissions. However, only a few percent of the source areas can transport fluxes to the catchment outlet. These effective source areas, together with the main transmission areas are potential candidates for improved management practices. In accordance with the critical area concept, it was shown that intervention with better management practices on a properly selected small proportion of the total area (1-3%) is sufficient to reach a remarkable improvement in water quality. If soil nutrient management is also considered in addition to water quality, intervention on 4-12% of the catchment areas can fulfill both aspects.

Balancing between retention and flushing in river networks--optimizing nutrient management to improve trophic state

River basin management can frequently involve decisive situations, when conflicting interests must be resolved. In the Zala River catchment (Western Hungary) local efforts to improve water quality by reducing algal biomass are not always harmonized with the requirement of sustaining the same objective in its recipient, Lake Balaton. The PhosFate catchment model is a GIS tool designed to estimate the spatial variability and fate of diffuse phosphorus emission during transport. Besides diffuse pollution, a simplified annual hydrologic balance is also calculated. A new module was added to PhosFate that tracked the development of entrained algae during their travel downstream. The extended model was used to simulate the current average algal concentrations in the river network. The numerous small reservoirs and impoundments on the tributaries of the Zala River were identified as the key elements in determining algal biomass, since they fundamentally increase the water residence time (WRT) in the system. Without reservoirs, the short WRT in the drainage network would successfully prevent the development of suspended algal biomass despite the fairly high SRP concentrations. However, the removal of such standing waters is impossible for socio-economic reasons and reducing the overall P load to Lake Balaton would also require increasing WRT in the system. As a resolution to these conflicting interests, a hybrid management strategy was designed to simultaneously reach both goals: (i) switching from WRT to P limitation in reservoirs responsible for most of algal growth, and (ii) optimized deployment of buffer zones and the introduction of best agricultural practices on the remaining majority of the catchment to reduce the overall P load. The suggested management approach could be applied in other river catchments too, due to the extensive presence of reservoirs and impoundments in many stream networks.