PHOSPHORUS CONTROL STRATEGIES

There are many recognized water quality problems resulting from nonpoi nt entry of P into surface waters. It has only been in the last decade that P applied to land as animal waste has been recognized as a large potential problem. This problem is a result of the concentration of a nimals into a small area to the extend that so much waste is applied t o land that the P fixing capacity of the soil is exceeded. One of the first areas where this problem was recognized was in the Lake Okeechob ee drainage basin. When the sources of P in the lake were identified, regulators took action to have best management practices (BMP) impleme nted on dairies which were a primary source of P and also several rese arch projects were initiated to determine if better BMP could be devel oped. One of the most successful BMPs thus far implemented is improvem ent of collection of waste in high intensity areas and routing this wa ste to improved lagoons. Preliminary data indicate that up to 90% of t he P entering a lagoon system remains there in the sludge. A project t o remove the P with a combination of chemical and biological reactions has also been successful thus far. It has been shown that aquatic mac rophytes can be utilized to reduce the P moving from secondary lagoons toward the drainage canals. There is, however, a problem of what to d o with the plants. The model LOADSS has been successful in predicting the effect of various management options in the watershed on amount of P which will enter the lake. If the management options described in t his special issue of Ecological Engineering are not successful in redu cing the P loads in the lake to acceptable limits, it may mean that la rge animal units should not be concentrated in many watersheds of the U.S. because of the probability of encountering P problems.