Compost is well known as an amendment for formulating potting blends and improving the productivity of soils. Less well known is its efficiency as a filter.
As an air filter, mature compost is helpful in the break down of biosolids and other odoriferous materials. Large commercial composting facilities force air through the compost piles to hasten the process. To filter the air, the ends of the exhaust pipe are covered with compost.
Compost is also a very effective water filter. Silt fences surrounding construction sites filter out only sand and silt. Clay and nutrients flow through these fences. Placing a berm of compost on the low side of silt fences adds the capacity to filter out clays and nutrients. Compost contains both positive and negative charges that attract both positively and negatively charged elements and clays. Seeding the compost with a vigorously growing grass such as K-31 tall fescue prevents the compost from accumulating excess levels of nutrients.
Adding compost berms should be compulsory in all construction sites where silt fences are mandatory. Mesh tubes filled with compost can be used in place of building berms of compost. Filtrex is a mesh tube filled with compost that is laid on the low side of a silt fence. The tube is available in different diameters, with some tubes equipped with an apron that directs the water through the tube. Filtrex was recently used on a highway construction site on Rt. 214 between Mayo and Muddy Creek roads. I have seen it used to stop stream bank erosion.
When you see brown water in the Bay, you need not look far to find a source of pollution in construction sites or a field that has not been planted with a cover crop. The brown color is clay in suspension. The clay most likely contains phosphorus as well as other nutrients. The turbidity, which will last several weeks, caused by clay in suspension, prevents sunlight from penetrating to the bottom of the Bay where aquatic vegetation grows. The nutrients that enter the water with the clay encourage the growth of algae.