MM-7A (6/29/05 version)
Overland Transport Management Practice Systems
Overview
The management practices selection process provides guidance on how to link the appropriate type, or category, of management practices (MPs) to the identified NPS problem. Once this linkage and appropriate selection has been made, it is usually necessary to integrate multiple practices into a systems approach.
An overland transport management practice system is any combination of MPs that are used together to comprehensively control a pollutant from the same source. However, properly designed MP systems are just part of the NPS control strategy. MP systems must also be placed in the correct locations in the watershed (targeted pollutant source areas) and the extent of implementation must be sufficient to achieve water quality improvements.
Specifically, overland transport of pollutants to surface and ground water can be controlled by:
- reducing the pollutant load at the source; and/or
- retarding the transport of pollutant to the water resource (either by reducing the amount of runoff or through chemical or biological transformation);
MP systems are generally more effective at controlling NPS pollution than individual MPs because:
- MP systems minimize the impact of the pollutant at the source, during the overland transport process, and in the water body;
- MP systems can be used at two or more points in the pollutant delivery system.
These preventative approaches are preferable, and often less costly, than reclamation of a site after the pollutant has entered the water resource.
Application of an Overland Transport Management Practice System
When a pollutant is derived from more than one source, a separate overland MP system should be designed to reduce pollutant loss from each source. Although a management practice may be designed to control one type of pollutant, it can also provide secondary benefits by controlling other pollutants, depending on how the pollutants are generated or transported. For example, practices that reduce erosion and sediment delivery often reduce phosphorus losses since phosphorus is strongly adsorbed to silt and clay particles.
In contrast, some overland transport management practices used to control one pollutant may inadvertently increase the generation, transport, or delivery of another pollutant. Because conservation tillage creates increased soil porosity (i.e., large pore spaces), it may increase nitrate leaching through the soil, particularly when the amount and timing of nitrogen application is not considered during implementation. Tile drains, used to reduce overland runoff and increase soil drainage, can also have the undesirable effect of concentrating and delivering nitrogen directly to streams. To reduce the nitrogen pollution caused by tile drains, other management practices, such as nutrient management, precision agriculture practices for source reduction, and/or biofilters to intercept tile drain outflow, may be needed.
Drainage tile system outlets and inputs are often a forgotten possible source of potential aquatic life use impairment, particularly for nutrients. Evaluation of these systems and their nutrient inputs should be a consideration of any restoration or management plan. Without this consideration, restoration efforts may be negated by the direct release of nutrients from subsurface tiles, inadequately treated wastewater from household sewage treatment systems, or agricultural fields with excess nutrients. Drainage management systems and nutrient management are practices that could be evaluated for restoration effectiveness.
Evaluating Options, Overland Transport Management Practice Systems
There are two types of overland transport managment practice systems:
Repetitive Pollutant Reduction Systems
Systems that combine individual management practices to address a pollutant or pollutants at different points in the pollutant delivery process achieve management objectives through repetitive pollution reductions. For example, a combination of conservation tillage, grassed waterways, field borders, and sediment retention basins control soil particles and runoff at various stages in the agricultural pollutant delivery process. A combination of nutrient management, conservation tillage, field borders, and riparian buffers provide similar and repetitive functions to control nitrogen losses from agricultural operations.
Necessary Diversification Pollutant Reduction Systems
Necessary diversification occurs when a management practice cannot be used without an accompanying practice. For example, fence installation to eliminate livestock in the stream is a common practice to reduce or eliminate sediment and nutrient pollution. However, for this to be a practical management option, offstream watering devices may be needed to provide an alternative drinking water source for the livestock.
Site-Specific Design, Overland Flow Management Practice Systems
There is no single, ideal management practice system for controlling a particular pollutant or combination of pollutants in all situations. However, management practice systems must be selected, designed, implemented, and maintained in accordance with site-specific considerations to insure that the practices function together to achieve the overall management goals. The system should be designed based on:
- the type of pollutant;
- the source of the pollutant;
- the cause of the pollution at the source;
- the land use, climactic, and environmental conditions;
- the pollution reduction goals;
- the economic situation of the landowner;
- the experience of the system designers; and
- the willingness and ability of the landowner to implement and maintain the practices.
The relative importance of these and other factors will vary depending upon other considerations, such as whether the implementation is voluntary or mandatory.
References
Gale, J.A., D.E. Line, D.L. Osmond, S.W. Coffey, J. Spooner, J.A. Arnold, T.J. Hoban, and R.C. Wimberley. 1993. Evaluation of the Experimental Rural Clean Water Program. National Water Quality Evaluation Project, NCSU Water Quality Group, Biological and Agricultural Engineering Department, North Carolina State University, Raleigh, NC, (published by U.S. Environmental Protection Agency) EPA-841- R-93-005, 559p.
NRCS. 1994. National Handbook of Conservation Practices. Natural Resources Conservation Service (formerly Soil Conservation Service), U.S. Department of Agriculture, Washington, DC.