Atmospheric Deposition of Phosphorus to the Everglades: Concepts, Constraints, and Published Deposition Rates for Ecosystem Management

Abstract

This paper summarizes concepts underlying the atmospheric input of phosphorus (P) to ecosystems, published rates of P deposition, measurement methods, and approaches to future monitoring and research. P conveyed through the atmosphere can be a significant nutrient source for some freshwater and marine ecosystems. Particle sources and sinks at the land-air interface produce variation in P deposition from the atmosphere across temporal and spatial scales. Natural plant canopies can affect deposition rates by changing the physical environment and surface area for particle deposition. Land-use patterns can alter P deposition rates by changing particle concentrations in the atmosphere. The vast majority of P in dry atmospheric deposition is conveyed by coarse (2.5 to 10 μm) and giant (10 to 100 μm) particles, and yet these size fractions represent a challenge for long-term atmospheric monitoring in the absence of accepted methods for routine sampling. Most information on P deposition is from bulk precipitation collectors and wet/dry bucket sampling, both with questionable precision and accuracy. Most published annual rates of P deposition are gross estimates derived from bulk precipitation sampling in locations around the globe and range from about 5 to well over 100 mg P m year, although most inland ecosystems receive between 20 and 80 mg P m year. Rates below 30 mg P m year are found in remote areas and near coastlines. Intermediate rates of 30 to 50 mg P m year are associated with forests or mixed land use, and rates of 50 to 100 mg P m year or more are often recorded from urban or agricultural settings. Comparison with other methods suggests that these bulk precipitation estimates provide crude boundaries around actual P deposition rates for various land uses. However, data screening cannot remove all positive bias caused by contamination of bucket or bulk collectors. As a consequence, continued sampling with these standard collectors in a region will not reduce the large uncertainty in rates derived from existing data. Calibrated surface accumulation methods hold promise as a primary means to estimate P flux in future monitoring. New methods for long-term P deposition monitoring will require an intercomparison of P flux estimates from surrogate surfaces, impactor sampling of particle concentrations combined with deposition models, and “throughfall” estimates for natural canopies. With better sampling methods and more long-term monitoring data, the importance of atmospheric P deposition in ecosystem dynamics and management can be better understood and predicted.

Maintaining Tree Islands in the Florida Everglades: Nutrient Redistribution Is the Key

“…As noted earlier, atmospheric deposition (wetfall plus dryfall) was the primary source of P for the historic Everglades ecosystem (Davis 1994;Noe et al 2001 , with the interior of the peninsula experiencing the lowest deposition rates (Redfield 2002). Dry atmospheric deposition has not been measured on tree islands in the Everglades; however, we hypothesize that it should be considerably higher on islands because forest edges are very effective at trapping dry fallout (Weathers et al 2001;Redfield 2002) and tree islands are, in effect, mostly forest edges.…”

“…Dry atmospheric deposition has not been measured on tree islands in the Everglades; however, we hypothesize that it should be considerably higher on islands because forest edges are very effective at trapping dry fallout (Weathers et al 2001;Redfield 2002) and tree islands are, in effect, mostly forest edges. Dry deposition has been found to make substantial contributions to the nutrient cycles of many other wetland ecosystems (Blank et al 1999;Krah et al 2004).…”

Conductivity as a tracer of agricultural and urban runoff to delineate water quality impacts in the northern Everglades

“…Wet deposition of TP, TN, Cl and SO 4 were estimated from data collected for STA-1W (ENRWET), northwest of the Refuge. Contamination of the bucket used for wet deposition sample collection has been noted as an issue for data precision and accuracy (Walker and Jewell 1997;Redfield 2002), therefore we present median values (following Redfield 2002) to reduce some of the bias associated with sample contamination. Caution was exercised in interpreting wet deposition data given contamination and other issues with data reliability for wet deposition measurements (Redfield 2002).…”

Simulating Everglades National Park hydrology and phosphorus transport under existing and future scenarios using numerical modeling

“…Because ambient surface water phosphorus levels are so low, it is important to establish the background loading from atmospheric deposition. However, many factors influence the calculation of rate of deposition of phosphorus in the Everglades, including seasonal trends, proximity to anthropogenic activity, sample contamination, and sampling method (Redfield, 2002;Walker, 1999).…”

“…The rainfall mean P concentration 0.0017 mg/L, determined from Grimshaw and Dolske (2002), was used. A constant loading of 13.2 g/day of T P drydep (taken from (Redfield, 2002)) was applied over the entire domain as a daily uniform overland loading, representing the Dry Deposition of phosphorus and is included in the source term of the AD equation.…”