Critical Source Areas

The concept of Critical Source Areas, or CSAs, illustrate the biophysical need to for targeting to address NPS pollution. CSAs are areas in the Landscape that contribute disproportionately high pollutant levels and are the result of an interaction between two factors:  hydrologic flow patterns and pollutant loading patterns.csaimage

Hydrologic flow patterns can generate hydrologically sensitive areas (HSAs), which are areas in the landscape that are likely to become saturated due to soil characteristics and landscape slope characteristics (Qui 2009). Once these areas become saturated, they are more likely to produce overland runoff flow that will enter waterways. When HSAs correspond to areas in thsahe landscape that where pollutants may be found, such as agricultural fields, these HSAs will likely carry and distribute pollutants in their overland flow. The image to the right  shows the results of Qui’s 2009 study which applied the concept on a watershed scale in New Jersey. Qui’s study identified several upland CSA sites that are often overlooked in traditional buffer placement strategies, indicating its utility at providing insight for biophysical transport mechanisms.


Assessing Critical Source Areas in Watersheds

Qui, Z. 2009. Assessing Critical Source Areas in Watersheds for Conservation Buffer Planning and Riparian Restoration. Environmental Management 44: 968-980.

The focus of this paper is to utilize GIS tools to identify the efficient placement of conservation buffers to improve water quality. While the author also seeks to evaluate the economic efficiency of different buffer placement scenarios, the economic elements of his study are not as refined as other studies available. Qui’s methodology is to identify Hydrologically Sensitive Areas (HSAs), which are areas in the landscape that are likely to become saturated due to soil characteristics and will produce overland runoff due to topographic and/or land use characteristics. From there Critical Source Areas (CSAs) can be defined as HSAs that are likely to carry high levels of pollutants with them. This model is then applied to the Neshanic River watershed in the Raritan River Basin located in Hunterdon County, New Jersey, a 31 square mile watershed in which agricultural land is steadily being suburban and urbanized. The study finds that buffer placement can be most efficiently applied within the riparian areas of streams as well as upland beyond the riparian area. This study is valuable as it shows that relatively simple modeling can provide quite detailed results for at least certain targeting practices. While the scale of the results is slightly ambiguous, the author seems to be applying his results at the field level. It also shows how targeting of CSAs can be applied in an urbanizing watershed.

Conference Notes: MIssissquoi Bay Basin Project

Lake Champlain Basin Program. 2009. Missisquoi Bay Basin Project: Identifying Critical Source Areas of Pollution. Workshop Summary. Burlington, VT.

This workshop brought in professionals from throughout the Missisquoi Bay Basin on Lake Champlain to discuss CSA identification and targeting strategies. They began by asking participants to define CSAs and discuss methods, scales, and products in identifying them. Of those answering the first part, there was very little disagreement and the focus seems to generally be on modeling and mapping field scale CSAs. The discussion that follow focus largely on data needs and spatial analysis opportunities. They also discuss the importance of bringing in land managers and farmers, typically voluntarily, and incorporating local knowledge. This conference summary provides some useful general information on CSA identification and potential improvements.


Next: Disproportionality