While generally thought of and managed separately from streams and wetlands, a watershed’s uplands in many ways define the character of a river system. The development of uplands within a watershed can affect a wide range of important factors in aquatic systems, both directly and indirectly. Additionally, land use practices on both developed and undeveloped uplands can cause ecosystem stress.
The low-flow and migration barrier stressors discussed above are clearly linked to development, as are numerous other stressors not individually listed. In many ways, development could be considered one of the primary stressors (or the ultimate causes of stress) with more specific issues such as low-flows, flooding, and reduced stream continuity representing symptoms caused by development. How waterways are affected by individual development projects varies widely based on factors such as geology, distance to channel, and development design, but some generalizations can be made.
Development can cause direct loss and fragmentation of both aquatic and upland habitat. These impacts tend to be particularly acute in situations where development is close to waterways, wetlands or active floodplains, but any development in the watershed can have serious consequences for the region’s ecology.
A major issue with development is the increase in impervious surfaces within a watershed in the form of roofs, roads, parking lots, etc. Impervious surfaces impair groundwater recharge, as water tends to be quickly shunted via surface flow (stormwater) to streams, rivers and, in some cases, sewer systems. This has the combined effect of making streams “flashy” (that is prone to fast, extreme flooding events after precipitation) and more prone to low flows between precipitation events as groundwater aquifers are replenished at a slower rate. Since stormwater washes over impervious surfaces and doesn’t percolate through the ground it often exhibits more extreme temperatures and carries higher concentrations of pollutants to rivers and streams.
Land use practices on already developed properties, agricultural lands, and other actively managed landscapes can have serious impacts on water quality. Excess nutrients, especially nitrogen and phosphorus from fertilizers, can cause eutrophication of the rivers and the estuaries. Similarly, certain pesticides, petroleum products and other chemicals can make their way to waterways if not properly handled on uplands. Land use decisions can also lead to the introduction and establishment of populations of invasive species that can serve as sources for the spread of these species to nearby areas.
Consequences of Development
In general, development within a watershed and intensive (or poorly managed) land use practices often leads to reductions in native aquatic communities through a combination of factors. A 2011 study by the USGS and MassWildlife found that for every one percent increase in imperviousness, there is a 3.7% decrease in the abundance of river (fluvial) fish (Armstrong et al., 2011). Careful planning and strict adherence to best management practices for development projects and land management can substantially limit many impacts. Even the best development methods employed on previously undeveloped parcels will result in a net negative impact (such as increased impervious surfaces or decreased infiltration). With this in mind, it is important to protect key land from development, and look to opportunities to improve conditions through retrofitting and during redevelopment of properties in order to improve overall development impacts in a watershed.