Organic matter dynamics in the Florida coastal Everglades: A molecular marker and isotopic approach

Everglades National Park (ENP) is about to undergo the world's largest wetland restoration with the aim of improving the quality, timing and distribution of water flow. The changes in water flow are hypothesized to alter the nutrient fluxes and organic matter (OM) dynamics within ENP, especially in the estuarine areas. This study used a multi-proxy approach of molecular markers and stable δ 13C isotope measurements, to determine the present day OM dynamics in ENP. ^ OM dynamics in wetland soils/sediments have proved to be difficult to understand using traditional geochemical approaches. These are often inadequate to describe the multitude of OM sources (e.g. higher land plant, emergent vegetation, submerged vegetation) to the soils/sediments and the complex diagenetic processes that can alter the OM characteristics. A multi-proxy approach, however, that incorporates both molecular level and bulk parameter information is ideal to comprehend complex OM dynamics in aquatic environments. Therefore, biomass-specific molecular markers or proxies can be useful in tracing the sources and processing of OM. This approach was used to examine the OM dynamics in the two major drainage basins, Shark River Slough and Taylor River Slough, of ENP. Freshwater to marine transects were sampled in both systems for soils/sediments and suspended particulate organic matter (SPOM) to be characterized through bulk OM analyses, lipid biomarker determinations (e.g. sterols, fatty acids, hydrocarbons and triterpenoids) and compound-specific stable carbon isotope (δ 13C) determinations. ^ One key accomplishment of the research was the assessment of a molecular marker proxy (Paq) to distinguish between emergent/higher plant vegetation from submerged vegetation within ENP. This proxy proved to be quite useful at tracing OM inputs to the soils/sediments of ENP. A second key accomplishment was the development of a 3-way model using vegetation specific molecular markers. This novel, descriptive model was successfully applied to the estuarine areas of Taylor and Shark River sloughs, providing clear evidence of mixing of freshwater, estuarine and marine derived OM in these areas. In addition, diagenetic transformations of OM in these estuaries were found to be quite different between Taylor and Shark Rivers, and are likely a result of OM quality and hydrological differences. ^

Salinity and Chlorophyll a as Performance Measures to Rehabilitate a Mangrove-Dominated Deltaic Coastal Region: the Ciénaga Grande de Santa Marta–Pajarales Lagoon Complex, Colombia

Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures in the period 1999–2001 to evaluate the effect of a hydrological rehabilitation project in the Ciénaga Grande de Santa Marta (CGSM)–Pajarales lagoon complex, Colombia where freshwater diversions were initiated in 1995 and completed in 1998. The objective of this study was to evaluate how diversions of freshwater into previously hypersaline (>80) environments changed the spatial and temporal distribution of environmental characteristics. Following the diversion, 19 surveys and transects using a flow-through system were surveyed in the CGSM–Pajarales complex to continuously measure selected water quality parameters. Geostatistical analysis indicates that hydrology and salinity regimes and water circulation patterns in the CGSM lagoon are largely controlled by freshwater discharge from the Fundacion, Aracataca, and Sevilla Rivers. Residence times in the CGSM lagoon were similar before (15.5 ± 3.8 days) and after (14.2 ± 2.0 days) the rehabilitation project and indicated that the system is flushed regularly. In contrast, chl-a biomass was highly variable in the CGSM–Pajarales lagoon complex and not related to discharge patterns. Mean annual chl-a biomass (44–250 μg L−1) following the diversion project was similar to values recorded since the 1980s and still remains among the highest reported in coastal systems around the world owing to its unique hydrology regulated by the Magdalena River and Sierra Nevada de Santa Marta watersheds and the high teleconnection to the El Niño Southern Oscillation (ENSO). Our results confirm that the reduction in salinity in the CGSM lagoon and Pajarales complex during 1999–2000 was largely driven by high precipitation (2500 mm) induced by the ENSO–La Niña rather than by the freshwater diversions.

Spatiotemporal Variation in Abundance and Social Structure of Bottlenose Dolphins in the Florida Coastal Everglades

Bottlenose dolphins (Tursiops truncatus) are large-bodied predators that are locally abundant in the coastal Everglades. Because of their potential to exert strong top-down effects on their communities, it is important to understand how spatiotemporal variation in biotic and abiotic factors affects the abundance and behavior of dolphins. This study combined two years of transect surveys with photographic identification methods to assess spatiotemporal variation in the abundance and group sizes of bottlenose dolphins across four large regions of the coastal Everglades including the Shark and Harney Rivers, Whitewater Bay, and coastal oceans of the Gulf of Mexico and Florida Bay. Dolphin abundance was similar across wet and dry seasons, except in river habitats where abundances were higher during the dry season. Group sizes were largest in Florida Bay and open water. Dolphins may be relatively resilient to abiotic changes in the coastal Everglades, with the possible exception of river habitats.

Seasonal fish community variation in headwater mangrove creeks in the southwestern Everglades: an examination of their role as dry-down refuges

The connectivity between the fish community of estuarine mangroves and that of freshwater habitats upstream remains poorly understood. In the Florida Everglades, mangrove-lined creeks link freshwater marshes to estuarine habitats downstream and may act as dry-season refuges for freshwater fishes. We examined seasonal dynamics in the fish community of ecotonal creeks in the southwestern region of Everglades National Park, specifically Rookery Branch and the North and watson rivers. Twelve low-order creeks were sampled via electrofishing, gill nets, and minnow traps during the wet season, transition period, and dry season in 2004-2005. Catches were greater in Rookery Branch than in the North and watson rivers, particularly during the transition period. Community composition varied seasonally in Rookery Branch, and to a greater extent for the larger species, reflecting a pulse of freshwater taxa into creeks as marshes upstream dried periodically. The pulse was short-lived, a later sample showed substantial decreases in freshwater fish numbers. No evidence of a similar influx was seen in the North and watson rivers, which drain shorter hydroperiod marshes and exhibit higher salinities. These results suggest that head-water creeks can serve as important dry-season refugia. Increased freshwater flow resulting from Everglades restoration may enhance this connectivity.

Using Optical Properties to Quantify Fringe Mangrove Inputs to the Dissolved Organic Matter (DOM) Pool in a Subtropical Estuary

Dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) optical properties were analyzed along two estuarine river transects during the wet and dry seasons to better understand DOM dynamics and quantify mangrove inputs. A tidal study was performed to assess the impacts of tidal pumping on DOM transport. DOM in the estuaries showed non-conservative mixing indicative of mangrove-derived inputs. Similarly, fluorescence data suggest that some terrestrial humic-like components showed non-conservative behavior. An Everglades freshwater-derived fluorescent component, which is associated with soil inputs from the Northern Everglades, behaved conservatively. During the dry season, a protein-like component behaved conservatively until the mid-salinity range when non-conservative behavior due to degradation and/or loss was observed. The tidal study data suggests mangrove porewater inputs to the rivers following low tide. The differences in quantity of DOM exported by the Shark and Harney Rivers imply that geomorphology and tidal hydrology may be a dominant factor controlling the amount of DOM exported from the mangrove ecotone, where up to 21 % of the DOC is mangrove-derived. Additionally, nutrient concentrations and other temporal factors may control DOM export from the mangroves, particularly for the microbially derived fluorescent components, contributing to the seasonal differences. The wet and dry season fluxes of mangrove DOM from the Shark River is estimated as 0.27 × 109 mg C d−1 and 0.075 × 109 mg C d−1, respectively, and the Harney River is estimated as 1.9 × 109 mg C d−1 and 0.20 × 109 mg C d−1.