Present and Past Nutrient Dynamics of a Small Pond in Southwest Florida

Nutrient dynamics of a small pond in southwest Florida were modeled in space and time. The primary storage compartment of the system is the sediments, and the primary sources and sinks for nutrients are the atmosphere and ground water. Of the 93 g per yr of phosphorus entering the pond, primarily as bulk precipitation, approximately 69 percent is stored within the system and the remainder leaves through the groundwater. About 2400 g of nitrogen enter the pond annually and of this 12 percent and 5 percent exit the system via atmosphere and ground water, respectively.

The pond's age, determined by radiocarbon dating, is approximately 5000 years, and during this time the sediments have accumulated 124 kg of phosphorus and 3,140 kg of nitrogen. The atmosphere and ground have made a net contribution (input minus output) of about 124 kg of phosphorus and 3600 kg of nitrogen during the past 5000 years, based on present-day rates and estimated changes in the sizes of the receiving surfaces. The remainder, in the case of nitrogen, is assumed to be atmospheric loss.

The importance of the groundwater sink for phosphorus is demonstrated, and its potential role as a nutrient input source for surface-water discharge boundaries is discussed.

Comparison of the annual atmospheric phosphorus input rate to the results of other researchers seems to indicate that the present-day rate may be spatially constant for undisturbed regions. The 5000-year budget for the study pond indicates that the preindustrial atmospheric input rate was about 27 mg per square meter per year, about 20 percent less than today's rate. This figure may be close to the preindustrial global rate.

It should be noted that when doing chemical analysis of environmental parameters, quality control is of the utmost importance. A discussion of quality control procedures is included in this work.

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