Matthew J. Cohen

FLORISTIC QUALITY INDICES FOR BIOTIC ASSESSMENT OF DEPRESSIONAL MARSH CONDITION IN FLORIDA

Evaluation of wetland ecological condition requires quantitative biological indices for measuring anthropogenic impairment. We implemented a modified floristic qual- ity assessment index (FQAI) protocol for 75 isolated, depressional herbaceous wetland systems, exploring refinements of FQAI standard methods. Species encountered during sampling (n = 397) were assigned coefficients of conservatism (CC) by ten expert botanists working independently. A quantitative summary metric of adjacent site buffer (up to 100 m) land use intensity, called the landscape development intensity (LDI) index, was cal- culated for each wetland system to quantify expected anthropogenic impairment. The as- sociation between LDI and wetland community mean CC scores was strong and condi- tionally independent of ecoregion. Weaker associations with LDI were observed for other community summary metrics, including richness-weighted FQAI. We inverted LDI to com- pute an intensity coefficient (IC), which quantifies observed buffer development intensity tolerated by each species. IC scores were significantly associated with CC scores on a species basis and strongly associated on a site mean basis. Growing interest in floristic quality assessment for regulatory purposes provides opportunities for formally linking expert opinion and ground observations of species-specific disturbance tolerance.

Do geographically isolated wetlands influence landscape functions

Geographically isolated wetlands (GIWs), those surrounded by uplands, exchange materials, energy, and organisms with other elements in hydrological and habitat networks, contributing to landscape functions, such as flow generation, nutrient and sediment retention, and biodiversity support. GIWs constitute most of the wetlands in many North American landscapes, provide a disproportionately large fraction of wetland edges where many functions are enhanced, and form complexes with other water bodies to create spatial and temporal heterogeneity in the timing, flow paths, and magnitude of network connectivity. These attributes signal a critical role for GIWs in sustaining a portfolio of landscape functions, but legal protections remain weak despite preferential loss from many landscapes. GIWs lack persistent surface water connections, but this condition does not imply the absence of hydrological, biogeochemical, and biological exchanges with nearby and downstream waters. Although hydrological and biogeochemical connectivity is often episodic or slow (e.g., via groundwater), hydrologic continuity and limited evaporative solute enrichment suggest both flow generation and solute and sediment retention. Similarly, whereas biological connectivity usually requires overland dispersal, numerous organisms, including many rare or threatened species, use both GIWs and downstream waters at different times or life stages, suggesting that GIWs are critical elements of landscape habitat mosaics. Indeed, weaker hydrologic connectivity with downstream waters and constrained biological connectivity with other landscape elements are precisely what enhances some GIW functions and enables others. Based on analysis of wetland geography and synthesis of wetland functions, we argue that sustaining landscape functions requires conserving the entire continuum of wetland connectivity, including GIWs.

Diel phosphorus variation and the stoichiometry of ecosystem metabolism in a large spring‐fed river

Elemental cycles are coupled directly and indirectly to ecosystem metabolism at multiple time scales. Understanding coupling in lotic ecosystems has recently advanced through simultaneous high-frequency measurements of multiple solutes. Using hourly in situ measurements of soluble reactive phosphorus (SRP), specific conductance (SpC), and dissolved oxygen (DO), we estimated phosphorus (P) retention pathways and dynamics in a large (discharge, Q ≈ 7.5 m3/s) spring-fed river (Ichetucknee River, Florida, USA). Across eight multi-day deployments, highly regular diel SRP variation of 3–9 μg P/L (mean ∼50 μg P/L) was strongly correlated with DO variation, suggesting photosynthetic control directly via assimilation, and/or indirectly via geochemical reactions. Consistent afternoon SRP maxima and midnight minima suggest peak removal lags gross primary production (GPP) by ∼8 hours. Two overlapping processes were evident, one dominant with maximum removal near midnight, the other smaller with maximum removal near m...

Species diversity in the Florida Everglades, USA: A systems approach to calculating biodiversity

Abstract.The Everglades, a complex wetland mosaic bounded by human development at the southern tip of the Florida Peninsula, is home to a wide array of species, including 68 threatened or endangered animal species. Species richness within Everglades National Park, at the southern extreme of the Greater Everglades ecosystem, is 1033 plant taxa, 60 reptile taxa, 76 mammal taxa, 432 fish taxa, 349 bird taxa and 38 amphibian taxa. This paper briefly introduces the flora and fauna of the Greater Everglades, focusing on species of special conservation concern and those non-native species that are altering native ecology. While there is conservation utility in cataloging biodiversity, we argue that counts of species alone are inadequate descriptors of ecosystem condition because they fail to effectively indicate emergent ecosystem properties (resilience, productivity). We develop an approach to calculating biodiversity based on systems theory that can be applied across trophic levels to provide a condition benchmark that accounts for food web interactions. The Everglades, for which detailed flow data between ecosystem components have been compiled as part of ongoing modeling efforts (DeAngelis et al., 1998), is among the few ecosystems globally for which this technique is currently feasible. Flow data are coupled with exogenous forcing energies (in emergy units – Odum, 1996) to compute transformity values (Odum, 1988) for biotic and abiotic components of an Everglades graminoid marsh community. We calculate across-trophic level biodiversity using the Shannon information equation applied to ecosystem emergy flows. Results suggest that the graminoid marsh is operating at 42% of theoretical maximum ecosystem flow diversity. By comparing observed flows with theoretical maximum flows, we provide a measure of component conservation value; we observe strong overlap between species with lower than expected emergy-based importance and those known to be currently threatened or endangered. A significant positive association between this conservation value and transformity in the marsh suggests systematic uppertrophic level biodiversity degradation.

Geographically isolated wetlands: Rethinking a misnomer

We explore the category “geographically isolated wetlands” (GIWs; i.e., wetlands completely surrounded by uplands at the local scale) as used in the wetland sciences. As currently used, the GIW category (1) hampers scientific efforts by obscuring important hydrological and ecological differences among multiple wetland functional types, (2) aggregates wetlands in a manner not reflective of regulatory and management information needs, (3) implies wetlands so described are in some way “isolated,” an often incorrect implication, (4) is inconsistent with more broadly used and accepted concepts of “geographic isolation,” and (5) has injected unnecessary confusion into scientific investigations and discussions. Instead, we suggest other wetland classification systems offer more informative alternatives. For example, hydrogeomorphic (HGM) classes based on well-established scientific definitions account for wetland functional diversity thereby facilitating explorations into questions of connectivity without an a priori designation of “isolation.” Additionally, an HGM-type approach could be used in combination with terms reflective of current regulatory or policymaking needs. For those rare cases in which the condition of being surrounded by uplands is the relevant distinguishing characteristic, use of terminology that does not unnecessarily imply isolation (e.g., “upland embedded wetlands”) would help alleviate much confusion caused by the “geographically isolated wetlands” misnomer.

Algal blooms and the nitrogen-enrichment hypothesis in Florida springs: evidence, alternatives, and adaptive management

Contradictions between system-specific evidence and broader paradigms to explain ecosystem behavior present a challenge for natural resource management. In Florida (U.S.A.) springs, increasing nitrate (NO3-) concentrations have been implicated as the cause of algal overgrowth via alleviation of N-limitation. As such, policy and management efforts have centered heavily on reduction of nitrogen (N) loads. While the N-limitation hypothesis appears well founded on broadly supported aquatic eutrophication models, several observations from Florida springs are inconsistent with this hypothesis in its present simplified form. First, NO3- concentration is not correlated with algal abundance across the broad population of springs and is weakly negatively correlated with primary productivity. Second, within individual spring runs, algal mats are largely confined to the headwater reaches within 250 m of spring vents, while elevated NO3- concentrations persist for several kilometers or more. Third, historic observations suggest that establishment of macroalgal mats often lags behind observed increases in NO3- by more than a decade. Fourth, although microcosm experiments indicate high thresholds for N-limitation of algae, experiments in situ have demonstrated only minimal response to N enrichment. These muted responses may reflect large nutrient fluxes in springs, which were sufficient to satisfy present demand even at historic concentrations. New analyses of existing data indicate that dissolved oxygen (DO) has declined dramatically in many Florida springs over the past 30 years, and that DO and grazer abundance are better predictors of algal abundance in springs than are nutrient concentrations. Although a precautionary N-reduction strategy for Florida springs is warranted given demonstrable effects of nutrient enrichment in a broad suite of aquatic systems worldwide, the DO-grazer hypothesis and other potential mechanisms merit increased scientific scrutiny. This case study illustrates the importance of an adaptive approach that explicitly evaluates paradigms as hypotheses and actively seeks alternative explanations.

A significant nexus: Geographically isolated wetlands influence landscape hydrology

Recent U.S. Supreme Court rulings have limited federal protections for geographically isolated wetlands (GIWs) except where a “significant nexus” to a navigable water body is demonstrated. Geographic isolation does not imply GIWs are hydrologically disconnected; indeed, wetland-groundwater interactions may yield important controls on regional hydrology. Differences in specific yield (Sy) between uplands and inundated GIWs drive differences in water level responses to precipitation and evapotranspiration, leading to frequent reversals in hydraulic gradients that cause GIWs to act as both groundwater sinks and sources. These reversals are predicted to buffer surficial aquifer dynamics and thus base flow delivery, a process we refer to as landscape hydrologic capacitance. To test this hypothesis, we connected models of soil moisture, upland water table, and wetland stage to simulate hydrology of a low-relief landscape with GIWs, and explored the influences of total wetland area, individual wetland size, climate, and soil texture on water table and base flow variation. Increasing total wetland area and decreasing individual wetland size substantially decreased water table and base flow variation (e.g., reducing base flow standard deviation by as much as 50%). GIWs also decreased the frequency of extremely high and low water tables and base flow deliveries. For the same total wetland area, landscapes with fewer (i.e., larger) wetlands exhibited markedly lower hydrologic capacitance than those with more (i.e., smaller) wetlands, highlighting the importance of small GIWs to regional hydrology. Our results suggest that GIWs buffer dynamics of the surficial aquifer and stream base flow, providing an indirect but significant nexus to the regional hydrologic system.

Reciprocal Biotic Control on Hydrology, Nutrient Gradients, and Landform in the Greater Everglades

Restoration can be viewed as the process of reestablishing both exogenous drivers and internal feedbacks that maintain ecosystems in a desirable state. Correcting exogenous and abiotic drivers is clearly necessary, but may be insufficient to achieve desired outcomes in systems with self-organizing biotic feedbacks that substantially influence ecological stability and timing of responses. Evidence from a broad suite of systems demonstrates the prevalence of biotic control over key ecosystem attributes such as hydroperiod, nutrient gradients, and landform that are most commonly conceived of as exogenously controlled. While a general theory to predict conditions under which biotic controls exert such strong feedbacks is still nascent, it appears clear that the Greater Everglades/South Florida landscape has a high density of such effects. The authors focus on three examples of biotic control over abiotic processes: hydroperiod and discharge controls exerted by peat accretion in the ridge-slough landscape; phosphorus (P) gradients that emerge, at least in part, from interactions between accelerated peat accretion rates, vegetation structure and fauna; and reinforcing feedbacks among land elevation, aquatic respiration, and carbonate dissolution that produce local and landscape basin structure. The authors propose that the unifying theme of biogeomorphic landforms in South Florida is low extant topographic variability, which allows reciprocal biotic modification of local site conditions via mechanisms of peat accretion (including via effects of landscape P redistribution on primary production) or limestone dissolution. Coupling these local positive feedbacks, which drive patch expansion, with inhibitory or negative feedbacks on site suitability at distance, which serve to constrain patch expansion, provide the mechanistic basis for landscape pattern formation. The spatial attributes (range and isotropy) of the distal negative feedback, in particular, control pattern geometry; elucidating the mechanisms and properties of these distal feedbacks is critical to restoration planning.

Reflectance spectroscopy for routine agronomic soil analyses

Near-infrared reflectance spectroscopy is a demonstrated tool for quantitative analysis of numerous soil properties. Reported advantages include analytical precision, predictive accuracy, and reduced costs and processing times. A library (N = 1933) representing all major soil orders in Florida was assembled from samples submitted to the University of Florida Extension Soil Testing Laboratory for routine testing during 2004-2005. High-resolution diffuse reflectance spectra from each sample in the visible/near infrared were used to predict observations made using standard laboratory analytical procedures for soil pH, Mehlich-1-extractable P, K, Ca, Mg, Cu, Mn, and Zn, percentage of organic matter, and saturated hydraulic conductivity (Ksat). Calibrations were immediately applicable for organic matter and Al, based on relative performance determinant values (RPD = standard deviation/standard error of validation > 2.0). Models for pH, P, Ca, and Ksat showed moderate accuracy (1.5 < RPD < 2.0), whereas those for K, Cu, Mg, Mn, Zn, and Fe exhibited low efficiency (RPD < 1.5), indicating a need for further refinement before near-infrared reflectance spectroscopy is a viable alternate method to standard laboratory procedures. Prediction of soil fertility and productivity based on published Florida soil diagnostic categories showed effective discrimination for pH, P Mg, Mn, Cu (phytotoxicity), and Ksat. Our study showed that prediction efficiency is a strong function of mean nutrient/analyte concentration in the soil. We further demonstrated that near-infrared reflectance spectroscopy error rates were comparable to, and in some cases smaller than, laboratory analytical error rates, suggesting that the observed low spectral prediction efficiency may be substantially because of uncertainty in the laboratory data.

On the potential for high-resolution lidar to improve rainfall interception estimates in forest ecosystems

Closing the gaps in the water budget of forested ecosystems is a first-order challenge, with immediate implications for regional water supply, ecosystem function, and landscape biogeochemistry. Rainfall interception by vegetated canopies can be as great as 50% of total rainfall. There is considerable uncertainty in predicting this ecosystem property, which makes it one of the primary constraints in spatial water budgeting. Interception is largely controlled by vertical structure and canopy gaps on a relatively small scale. Emerging remote sensing technologies, such as lidar (light detection and ranging), now offer an unprecedented opportunity to quantify canopy architecture in three dimensions across the landscape. Use of such high-resolution spatial data, along with improved rainfall interception models, will aid in ecosystem process studies and the development of tools and incentives that could influence land-use policy and decision making in the future.