Both landscape biophysical conditions and human use of landscapes affect soil and sediment status (defined as soilsediment quality, quantity, location, and transport; Apitz 2011). How these affect SPUs depends on whether sediment status is appropriate to the needs of a given endpoint. Understanding and managing the dynamic interactions of sediment status on a diverse range of endpoints at the landscape or watershed scale should be the focus of sediment management. Clearly, if EcoRA is to be adapted to assess the roles of sediment at the watershed scale, we must address the complexity of sediment-endpoint interactions, and these more complex pathways of hazard and exposure. Apitz (2011) seeks to provide a language and conceptual framework on which sediment ecological risk assessment or, more precisely, sediment-ecosystem regional assessment (SEcoRA), can be developed in support of that goal.
To protect endpoints within regions and watersheds, it is necessary to understand and manage soil-sediment and hydrodynamic processes at the field-and reach-scale, and to aggregate these processes to larger scales. To address such issues for the management of sediment impacts at the river basin scale, Apitz et al. ( 2010) adapted the hierarchical patch dynamics paradigm (HPDP) approach, used to address multiscale issues for invasive species management (Landis 2005). Calculation modules were developed that evaluate how interacting processes at the field and river reach scale affect field-scale sediment status and transport; these fieldand reach-scale factors were then aggregated and integrated in a Sediment Regional Risk Assessment (SRRA) model to evaluate regional-scale effects on aquatic endpoints (Apitz et al. 2010). This model was developed for the Environment Agency of England and Wales to support the development of sediment river basin management plans for European Water Framework Directive compliance. This multiple-scale, systematic, transparent, and adaptable model, a sedimentspecific adaptation of the Regional Risk Assessment approach (Landis 2005), ranks the risks and benefits of multiple sediment sources to a range of endpoints throughout a river basin in a spatially explicit manner. It evaluates the relative risks and benefits as a function of industry, land use, endpoint, habitat, or region in a spatially explicit manner, either retrospecitively (to evaluate sediment sources, risks, and benefits regionally) or prognostically (to evaluate the basinscale risks and benefits of policy changes and targeted mitigation options). Thus far, this is a pilot model, which requires testing and adaptation using case study data, either based on geographic information system and spreadsheetenabled approaches (as currently designed) or probabilistic models on landscape interactions.
SEcoRA, SRRA, and other frameworks and tools can be used to balance the benefits of landscape-scale service use against the sustainability of aquatic ecosystem services. However, sediments themselves are only one component of ecosystems; such models must not only be validated but also should be expanded to address not only the complexity of interactions among soil, sediment, and services, but also to fold in an increasing number of ecosystem components. We have our work cut out for us.