RPA – Resource Protection Area
(Published December 2003)
Stewardship, at least to some Native Americans, meant abiding by the philosophy “We do not inherit from our forefathers, we borrow from our children.” In the case of water quality in Chesapeake Bay, and more important for us locally, water quality in our local waterways, we are deeply in debt. Unless we all change our “business as usual” philosophy, the debt will grow and water quality will worsen as the population and number of septic systems increases.
One of the most important local actions necessary is to respect and abide by the 100-foot Resource Protection Area demanded by the Bay Act. Stated simply, human activities that lead to pollution must be stopped within 100 feet of the water, and severely restricted elsewhere. Pollution by the fertilizers (nutrients) nitrate and phosphate, the oxidized forms of nitrogen and phosphorous found in groundwater, is the most serious problem. In the Northern Neck, nitrate and phosphate are derived from homeowner and agricultural practices, mostly from fertilization and the discharge from septic systems. Nitrate and phosphate enter the groundwater as the result of infiltration, or the percolation of rain into the ground. Infiltrating water dissolves soluble substances like nitrate and phosphate as it moves down to the water table. The volume of water is immense, amounting to about one-third of our rainfall, or a little more than a foot of water each year. Nutrient laden groundwater, continually supplied by rainfall, continues to dissolve soluble substances as it flows “downhill” underground, discharging into the nearest waterway. Infiltration of rain is augmented by the discharge from septic systems. Groundwater discharge, unseen and commonly unrecognized, is the source of almost all the nitrate and phosphate that enter our waterways.
In the waterway, nitrate and phosphate fertilize the growth of tiny algae, which cloud the water and inhibit the growth of desirable submerged aquatic vegetation. In summer, the prolific growth of algae can contribute to anoxia, or loss of dissolved oxygen from the water. When the algae die they fall to the bottom and rot. Last summer (2002) the bottom water in many of our local waterways became anoxic, killing oysters and causing crabbers to move their pots into shallow water.
Reducing the use of fertilizer and maintaining septic systems is an extremely important goal, and although it will reduce the problem in the future, it will not affect the nitrate and phosphate already present in the groundwater. This is where the 100-foot RPA becomes critical. The only cost-effective way we know to “sop up” the nitrate and phosphate already in the groundwater (and continually being added) is for plants to utilize the nutrients before the marine algae get an opportunity to do so. If all the land close the water was “saturated” with plant roots, the plants themselves, along with microbial reactions in the root zone, would consume a great deal of the nitrate and phosphate in the groundwater before it could discharge into the waterways. The denser and deeper the root zone the better.
An ideal buffer on land consists of deep-rooted trees with an overlapping leaf canopy. As a generalization, the size of the leaf canopy of a plant is matched by the size of the root zone. Deep roots from large trees are able to intercept the groundwater, and some trees such as red maple and pine can tolerate periodic submergence of their roots as the water table rises and falls. Establishment of a complete leaf canopy from these kinds of trees, at least 100 feet wide, between the waterway and every septic system and agricultural field in the Northern Neck should be our goal. Large trees, which can have a wide canopy (and wide trunk spacing), pruned of their lower limbs, do not significantly block a homeowner’s view of the water.
Marine plants and marshes play exactly the same role as (riparian) buffer strips on land in consuming nutrients from the groundwater. In addition, marine grasses provide food and habitat for marine organisms and retard erosion. Marine grasses thus augment nutrient control provided by a riparian buffer on land.
An ideal sloping shoreline contains a diverse wetland plant flora from mid tide level (below which the marine plants will not grow) as far inland as the topography permits. For the next 100 feet the shoreline should contain large trees, shrubs and grasses. The canopy of the trees should overlap, but not overhang the shoreline and shade the marsh plants, which need full sunlight. Cliffed shorelines commonly do not permit marsh plants to become established, and although coconut logs have been used to help stabilize such shorelines, rip-rap and bulkhead are probably the only long-term solution to the erosion of cliffed shorelines, which is inevitable as sea level rises. Erosion needs to be controlled because it contributes nitrate and phosphate to the water along with sediment that further clouds the water and smothers bottom-dwelling organisms like oysters.
The NAPS web site contains stewardship tips that address many issues important to waterfront property owners and other citizens of the Northern Neck, as well as links to many web sites of interest such as SEAS (Shoreline Erosion Advisory Service).