Michael J. Chimney

The ecological–societal underpinnings of Everglades restoration

The biotic integrity of the Florida Everglades, a wetland of immense international importance, is threatened as a result of decades of human manipulation for drainage and development. Past management of the system only exacerbated the problems associated with nutrient enrichment and disruption of regional hydrology. The Comprehensive Everglades Restoration Plan (CERP) now being implemented by Federal and State governments is an attempt to strike a balance between the needs of the environment with the complex management of water and the seemingly unbridled economic growth of southern Florida. CERP is expected to reverse negative environmental trends by “getting the water right”, but successful Everglades restoration will require both geochemical and hydrologic intervention on a massive scale. This will produce ecological trade-offs and will require new and innovative scientific measures to (1) reduce total phosphorus concentrations within the remaining marsh to 10 µg/L or lower; (2) quantify and link ecolo...

Submerged aquatic vegetation-based treatment wetlands for removing phosphorus from agricultural runoff: response to hydraulic and nutrient loading.

Submerged aquatic vegetation (SAV) communities exhibit phosphorus (P) removal mechanisms not found in wetlands dominated by emergent macrophytes. This includes direct assimilation of water column P by the plants and pH-mediated P coprecipitation with calcium carbonate (CaCO3). Recognizing that SAV might be employed to increase the performance of treatment wetlands, we investigated P removal in mesocosms (3.7 m2) stocked with a mixture of taxa common to the region: Najas guadalupensis, Ceratophyllum demersum, Chara spp. and Potamogeton illinoensis. Three sets of triplicate mesocosms received agricultural runoff from June 1998 to February 2000 at nominal hydraulic retention times (HRTs) of 1.5, 3.5 or 7.0 days. Mean total P (TP) loading rates were 19.7. 8.3 and 4.5 g/m2/yr. After eight months of operation. N. guadalupensis dominated the standing crop biomass and P storage, whereas C. demersum exhibited the highest tissue P content. Chara spp. was prominent only in the 7.0)-day HRT treatments while P. illinoensis largely disappeared. Inflow soluble reactive phosphorus (SRP) (10 163 microg/L) was reduced consistently to near the detection limit (2 microg/L) in the 3.5- and 7.0-day HRT treatments, and to a mean of 9 microg/L in the 1.5-day HRT treatment. The mean inflow TP concentration (10(7) microg/L) was reduced to 52, 29 and 23 microg/L in the 1.5-, 3.5- and 7.0-day HRT treatments, respectively. Total P concentrations in new sediment (mean= 641, 408 and 459 mg/kg in the 1.5-. 3.5-, and 7.0-day HRT mesocosms, respectively) were much higher than in the muck soil used to stock the mesocosms (236 mg/ kg). The calcium content of new sediment was twice that of the muck soil (16.5% vs. 7.6%), demonstrating that CaCO3 production and, perhaps, coprecipitation of P occurred. We observed no nocturnal remobilization of SRP despite diel fluctuations in pH and dissolved oxygen. Mean outflow TP (21 microg/L) from a 147 ha SAV wetland (4-day nominal HRT) was similar to mean outflow TP in the 3.5-day and 7.0-day HRT treatments. The mesocosms adequately mimicked P removal and other important characteristics of the larger system and can be used to address research questions regarding treatment performance of full-scale SAV wetlands. Available data suggest that the incorporation of SAV communities into the stormwater treatment areas may benefit Everglades restoration.

Large-scale constructed wetlands for nutrient removal from stormwater runoff: An everglades restoration project

The South Florida Water Management District (SFWMD) constructed a wetland south of Lake Okeechobee to begin the process of removing nutrients (especially phosphorus) from agricultural stormwater runoff entering the Everglades. The project, called the Everglades Nutrient Removal (ENR) project, is a prototype for larger, similarly constructed wetlands that the SFWMD will build as part of the Everglades restoration program. This innovative project is believed to be one of the largest agricultural stormwater cleanup projects in the United States, if not in the world. This publication describes the ENR projects design, construction, and proposed operation, as well as the proposed research program to be implemented over the next few years.

Hurricane effects on a shallow lake ecosystem, Lake Okeechobee, Florida (USA)

This unique case study of Lake Okeechobee - a large, shallow and culturally eutrophic lake in south Florida - documents the effects of hurricanes on its water quality, sediment, phytoplankton and submersed aquatic vegetation (SAV). Three hurricanes (Frances and Jeanne in 2004 and Wilma in 2005) that swept directly over the lake led to a number of expected changes throughout the system: 1) high winds produced large seiches, strong waves and currents that redistributed bottom sediments and uprooted SAV and emergent macrophytes; 2) sediment disturbance resulted in increased suspended solids and nutrients in the water column, reduced Secchi transparency and affected SAV recovery, phytoplankton biomass and phytoplankton species dominance; and 3) heavy rainfall increased flows, nutrient loads and lake water levels. Changes in suspended solids, most nutrient concentrations, phytoplankton and SAV persisted for two years after the hurricanes. This persistence was attributed to unconsolidated surface sediment that increased in thickness because of the storms and was more easily resuspended during subsequent wind events. Drought conditions and low lake levels in the second year after the hurricanes led to some recovery of SAV, primarily in the form of the non-vascular musk grass (Chara spp.). The absence of high-intensity hurricanes in the near future should aid in SAV recovery and return the nearshore region to a macrophyte-dominated clear-water state. Our results demonstrate the importance of sediment disturbance and water levels in shallow lakes that are vulnerable to extreme weather events.

The response of a freshwater wetland to long-term “low level” nutrient loads - marsh efficiency

Abstract Total phosphorus (TP) and nitrogen (TN) mass balances were calculated for Boney Marsh, a subtropical constructed freshwater wetland located along the floodplain of the Kissimmee River in south Florida, USA. River water was diverted through the marsh for a 9-year period (1978–1986). Monthly mean retention rates were 0.03 and 0.41 g m −2 month −1 for TP and TN, respectively, for the period of record. Nutrient retention rates and nutrient loading rates were strongly correlated for TP but not for TN. Total phosphorus removal efficiencies were consistently higher than TN removal efficiencies at all times, and remained relatively unchanged during the entire study period. The subtropical marsh was a net positive sink for TP year-round but not for TN. Boney Marsh nutrient assimilation capacity remained high and invariable for the period of record for TP but not for TN. Our analysis showed that studies which derive nutrient removal estimates from reductions in surface water concentrations, rather than mass balances, may under-represent mass retention by as much as 50 and 100% for TP and TN, respectively. Rainfall contributions to Boney Marsh nutrient budgets could be as high as 99 and 94% for TP and TN, respectively, depending on the season. An apparent net settling velocity for total phosphorus of 9.93 m year −1 provided independent confirmation of settling rates previously estimated for the Water Conservation Areas of southern Florida.

Minimizing phosphorus release from newly flooded organic soils amended with calcium silicate slag: a pilot study

A pilot study was conducted using commercially available forms of calcium silicate (CaSiO3) slag as a soil amendment to reduce phosphorus (P) release from an organic soil after flooding. Broadcasting CaSiO3 slag on top of the soil reduced the flux of soil P up to 84% compared to an unamended soil control. However, incorporation of CaSiO3 slag into the soil was only minimally effective at reducing P release. These materials have a potential use in the construction of treatment wetlands in south Florida. Further work is needed to better define reaction mechanisms, investigate the long-term treatment efficacy of these materials and address other environmental questions concerning their use.

Instar determination, length-mass and length-length relationships for the larvae of Chaoborus punctipennis Say from a southeastern (USA) cooling reservoir

Instar determination, length-mass and length-length relationships for Chaoborus punctipennis Say lar vae from a southeastern (USA) reservoir are described. Only head capsule length proved useful in determining instar stage. Power functions best fit length-length relationships among head capsule length, thorax width and body length. Power functions of body length, total length and thorax width were the best predictors of larval dry and ash-free dry mass. Thorax width may be a more reliable predictor of mass since it is not influenced by curvature of the body as body-length measurements may be. Summary statistics for head and body dimensions and length-mass regressions from this study were comparable to data in the literature for C. punctipennis.

Surface Seiche and Wind Set-up on Lake Okeechobee (Florida, USA) During Hurricanes Frances and Jeanne

Abstract Hurricanes Frances and Jeanne (HF and HJ) passed over Lake Okeechobee, Fla., in September 2004. Strong winds produced a large surface seiche during both storms. The slope of the water surface reversed itself within 4 hrs as wind direction changed during HF, but shifted in only 2 hrs during HJ. The greatest water level difference was along the lakes north-south (N-S) axis during both storms (2.6 and 3.5 m, respectively). Differences between maximum wind set-up (storm surge) and set-down on the opposite shore indicated that the slope of the water surface was not symmetrical at the height of either storm. Using simple steady-state models, maximum wind set-up was forecast for opposing stations along the lakes N-S axis and compared to observed data and storm surge predictions by the SLOSH model. Steady-state model accuracy was not improved by using averaging periods >15 min in length or by lagging weather and water temperature data behind lake stage. Steady-state models calibrated to the data performed better than uncalibrated models. Prediction errors for maximum wind set-up during HF and HJ by SLOSH were comparable to errors in the steady-state models. While not a substitute for sophisticated hydrodynamic models like SLOSH and LOHM, properly calibrated steady-state models can provide lake managers with reasonable estimates of wind set-up. Future use of simple wind set-up models on Lake Okeechobee will require validation against data from other hurricanes.

Spatiotemporal changes in soil phosphorus characteristics in a submerged aquatic vegetation-dominated treatment wetland

In South Florida, stormwater treatment areas (STAs) are used to reduce phosphorus (P) in runoff from agricultural areas before water is discharged into the Everglades Protection Area. The Everglades STAs retain a significant amount of P and play an important role in Everglades restoration. Wetland soils generally are long-term sinks for P; therefore, the sustainability of STA treatment performance can be assessed by tracking changes in soil characteristics. This study evaluated the spatiotemporal changes in soil P and related physicochemical characteristics in the unconsolidated floc and underlying surface soil layer (0-10 cm) of a 920-ha submerged aquatic vegetation (SAV)-dominated wetland (STA-2 Cell 3). Physicochemical properties in soil cores collected in 2003, 2007, 2009, and 2015 were evaluated and compared using geostatistical methods. Results indicated a gradual increase in floc depth over time. Total P (TP) concentrations in the floc were significantly higher than in the surface soil. Slight but statistically nonsignificant increases of mean TP in floc were observed. There was a significant increase in P storage in the floc layer between 2003 and 2007, with more P stored in the surface soil layer. Interpolated maps showed consistently higher TP and P storage values in the floc and surface soil near inflow areas of the cell during all sampling events. Furthermore, the 2003 to 2015 change maps showed TP and P storage decreasing from inflow to outflow. Bulk density (BD) in floc was approximately half of surface soil BD. Significant decline in the percentage of ash-free dry weight (AFDW) in floc from 2003 to 2007 indicated an increase in mineral content. This is consistent with increases in total calcium (TCa) in the floc, which was up to four times higher than in the surface soil layer. This indicates that TCa plays a central role in defining the characteristics of SAV cells. Overall, despite the heterogeneity of sediment attributes in the system, temporal trends and spatial patterns were observed in the physicochemical characteristics of soils. These trends and patterns can be used to understand long-term changes in large-scale treatment wetlands. Such insights are useful for optimizing and sustaining the treatment performance of STAs.