Todd Z. Osborne

Assessment of the spatial distribution of soil properties in a northern everglades marsh

Florida Everglades restoration plans are aimed at maintaining and restoring characteristic landscape features such as soil, vegetation, and hydrologic patterns. This study presents the results from an exhaustive spatial sampling of key soil properties in Water Conservation Area 1 (WCA 1), which is part of the northern Everglades. Three soil strata were sampled: floc, upper 0- to 10-cm soil layer, and 10- to 20-cm soil layer. A variety of properties were measured including bulk density (BD), loss on ignition (LOI), total phosphorus (TP), total inorganic phosphorus (TIP), total nitrogen (TN), total carbon (TC), total iron (TFe), total magnesium (TMg), total aluminum (TAl), and total calcium (TCa). Interpolated maps and model prediction uncertainties of properties were generated using geostatistical methods. We found that the uncertainty associated with spatial predictions of floc, particularly floc BD, was highest, whereas spatial predictions of soil chemical properties such as soil Ca were more accurate. The resultant spatial patterns for these soil properties identified three predominant features in WCA 1: (i) a north to south gradient in soil properties associated with the predominant hydrological gradient, (ii) areas of considerable soil nutrient enrichment along the western canal of WCA 1, and (iii) areas of considerable Fe enrichment along the eastern canal. By using geostatistical techniques we were able to describe the spatial dynamics of soil variables and express these predictions with an acceptable level of uncertainty.

Temperature sensitivity of greenhouse gas production in wetland soils of different vegetation

Organic matter decomposition regulates rates of carbon loss (CO2 and CH4) in wetlands and has implications for carbon sequestration in the context of changing global temperature. Here we determined the influence of temperature and vegetation type on both aerobic and anaerobic decomposition of organic matter in subtropical wetland soils. As in many other studies, increased temperature resulted in higher rates of respiration and methanogenesis under both aerobic and anaerobic conditions, and the positive effect of temperature depended on vegetation (source of carbon substrate to soil). Under anaerobic incubations, the proportion of gaseous C (CO2 and CH4) lost as CH4 increased with temperature indicating a greater sensitivity of methanogenesis to temperature. This was further supported by a wider range of Q10 values (1.4–3.6) for methane production as compared with anaerobic CO2 (1.3–2.5) or aerobic CO2 (1.4–2.1) production. The increasing strength of positive linear correlation between CO2:CH4 ratio and the soil organic matter ligno-cellulose index at higher temperature indicated that the temperature sensitivity of methanogenesis was likely the result of increased C availability at higher temperature. This information adds to our basic understanding of decomposition in warmer subtropical and tropical wetland systems and has implications for C models in wetlands with different vegetation types.

Phosphorous Cycling in the Greater Everglades Ecosystem: Legacy Phosphorous Implications for Management and Restoration

Phosphorus (P) retention in wetlands is an important function of watershed nutrient cycling, particularly in drainage basins with significant nonpoint nutrient contributions from agriculture and urban sources. Phosphorus storage involves complex interrelated physical, chemical, and biological processes that ultimately retain P in organic and inorganic forms. Both short-term storage of P mediated by assimilation into vegetation, translocation within above- and below-ground plant tissues, microorganisms, periphyton, and detritus, and long-term storage (retention by inorganic and organic soil particles and net accretion of organic matter) need to be considered. Here, we review and synthesize recent studies on P cycling and storage in soils and sediments throughout the Greater Everglades Ecosystem and the influence of biotic and abiotic regulation of P reactivity and mobility as related to restoration activities in south Florida. Total P storage in the floc/detrital layer and surface soils (0–10 cm) is estimated to be 400,000 metric tons (mt) within the entire Greater Everglades Ecosystem, of which 40% is present in the Lake Okeechobee Basin (LOB), 11% in sediments of Upper Chain of Lakes, Lake Istokpoga, and Lake Okeechobee, 30% in the Everglades Agricultural Area (EAA), and 19% in the Stormwater Treatment Areas (STAs) and the Everglades. Approximately, 35% of the P stored is in chemically nonreactive (not extractable after sequential extraction with acid or alkali) pool and is assumed to be stable. Phosphorus leakage rates from LOB and EAA are approximately 500 and 170 mt P per year, respectively, based on long-term P discharges into adjacent ecosystems. The estimated reactive P in the LOB soils is 65% of the total P, of which only 10 –25% is assumed to leak out of the system. Under this scenario, legacy P in LOB would maintain P loads of 500 mt per year to the lake for the next 20– 50 years. Similarly, surface soils of the EAA are estimated to release approximately 170 mt P per year for the next 50–120 years. The role of the STAs in reducing loads to downstream regions is critical and requires effective management of P forms to ensure the P is stabilized in these systems by the addition of chemical amendments or by dredging of accumulated soils. Also, additional efforts to minimize leakage of the legacy P from the northern regions should also be evaluated to reduce external P loading loads to the STAs.

CHARACTERIZATION OF THE SPATIAL DISTRIBUTION OF SOIL PROPERTIES IN WATER CONSERVATION AREA 2A, EVERGLADES, FLORIDA

Wetland soils are heterogenous in nature, and biogeochemical properties show different spatial autocorrelation structures that translate into fine- and coarse-scale spatial patterns. Understanding these patterns and how they relate to other ecosystem properties (e.g., vegetation) is critical to restore wetlands impacted by nutrient influx. Our goal was to investigate Water Conservation Area 2A, a wetland in the Florida Everglades, that has been impacted by nutrient influx and incursions of cattail as well as biogeochemical cycling of nutrients, hydrologic manipulation, and natural events (fire, hurricanes, and tropical storms). The objective of this study was to characterize the spatial patterns of soil and floc/detritus total phosphorus (TP), total inorganic phosphorus (TPi), bulk density (BD), total nitrogen (TN), total calcium (TCa), total carbon (TC), and floc depth in Water Conservation Area 2A. A total of 111 sites were sampled at three different depths (floc, 0- to 10-cm, and 10- to 20-cm depth). Geostatistical techniques were used to estimate and map soil properties across the wetland. Observed TP ranged from 155 to 1702 mg kg−1 (0-10 cm) with a mean of 551 mg kg−1 and showed strong spatial autocorrelation extending over long distances of 6864 m (10-20 cm) and 9669 m (floc). The nugget-to-sill ratio was less than 25% for all observed properties except for TN, indicating strong spatial dependence. This spatially explicit study provided insight into the variability of soil properties generated by external and internal factors and establishes a baseline framework for future management decisions involving the restoration of this wetland.

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.

Landscape Patterns of Significant Soil Nutrients and Contaminants in the Greater Everglades Ecosystem: Past, Present, and Future

The primary goal of this review and synthesis effort is to summarize present landscape patterns of key soil constituents such as carbon (C), phosphorus (P), sulfur (S), and mercury (Hg), all of which are of historical and present interest with respect to Everglades restoration. A secondary goal is to highlight the importance of landscape scale monitoring and assessment of soils in the Everglades Protection Area (EPA) with respect to present and future restoration efforts. Review of present information derived from the two independent landscape scale studies revealed significant patterns of soil thickness, organic matter, and P in the EPA. Two soil constituents of concern, Hg (biological toxicity) and S (linked to increased P cycling), also exhibit spatial patterns at the landscape scale, suggesting a need for focused efforts of restoration. Significant patterns of soil enrichment and change suggest a dynamic interaction between environmental stressors and soil biogeochemical properties across the landscape. Trends and patterns at the landscape scale in the EPA suggest that landscape scale monitoring and assessment is necessary and critical to determining the success of restoration efforts. However, several key questions, surrounding appropriate temporal and spatial sampling scales, the standardization of sampling methods, and the significance of short range variability must be addressed to facilitate future landscape scale assessment efforts.

Facilitating your replacement? Ecosystem engineer legacy affects establishment success of an expanding competitor.

Interactions with resident species can affect the rate that expanding species invade novel areas. These interactions can be antagonistic (biotic resistance), where resident species hinder invasive establishment, or facilitative (biotic assistance), where residents promote invasive establishment. The predominance of resistance or assistance could vary with the abiotic context. We examined how the effects of a resident ecosystem engineer interact with abiotic stress to resist or assist the establishment of an expanding competitor. In Florida salt marshes, native cordgrass, Spartina alterniflora, is an influential ecosystem engineer that, when dead, exerts a legacy effect by forming persistent wrack patches. We examined how the legacy effect of Spartina wrack varies with spatial context and abiotic conditions to influence establishment of the northward-expanding black mangrove, Avicennia germinans. Field surveys documented that Spartina wrack and Avicennia propagules co-occur in the high intertidal zone, and we conducted two outdoor mesocosm experiments to investigate this association. Wrack positively affected propagule establishment when propagules were beneath wrack, but negatively affected establishment when propagules were above wrack. The abiotic tidal regime influences the magnitude of wrack effects by controlling ambient moisture, and the positive and negative effects of wrack were stronger in low moisture conditions that simulated desiccation stress during harsh neap tides. Thus, the same resident engineer can either resist or assist an expanding competitor and the magnitude of these effects depends on abiotic conditions. We propose that under harsh conditions, there is greater scope for an engineer’s mediating influence to affect associated species, both positively and negatively.

From lake to estuary, the tale of two waters: a study of aquatic continuum biogeochemistry

The balance of fresh and saline water is essential to estuarine ecosystem function. Along the fresh-brackish-saline water gradient within the C-43 canal/Caloosahatchee River Estuary (CRE), the quantity, timing and distribution of water, and associated water quality significantly influence ecosystem function. Long-term trends of water quality and quantity were assessed from Lake Okeechobee to the CRE between May 1978 and April 2016. Significant changes to monthly flow volumes were detected between the lake and the estuary which correspond to changes in upstream management. and climatic events. Across the 37-year period, total phosphorus (TP) flow-weighted mean (FWM) concentration significantly increased at the lake; meanwhile, total nitrogen (TN) FMW concentrations significantly declined at both the lake and estuary headwaters. Between May 1999 and April 2016, TN, TP, and total organic carbon (TOC), ortho-P, and ammonium conditions were assessed within the estuary at several monitoring locations. Generally, nutrient concentrations decreased from upstream to downstream with shifts in TN/TP from values > 20 in the freshwater portion, ~ 20 in the estuarine portion, and < 20 in the marine portion indicating a spatial shift in nutrient limitations along the continuum. Aquatic productivity analysis suggests that the estuary is net heterotrophic with productivity being negatively influenced by TP, TN, and TOC likely due to a combination of effects including shading by high color dissolved organic matter. We conclude that rainfall patterns, land use, and the resulting discharges of runoff drive the ecology of the C-43/CRE aquatic continuum and associated biogeochemistry rather than water management associated with Lake Okeechobee.

Stoichiometric relationships amongst ecosystem compartments of a subtropical treatment wetland

Evaluation of carbon (C), nitrogen (N) and phosphorus (P) ratios in aquatic and terrestrial ecosystems can advance our understanding of biological processes, nutrient cycling and the decomposition of organic matter. This study investigated wetland nutrient stoichiometry within water column, soil flocculent material, recently accreted soil, and dominate vegetation within two treatment cells of the Everglades Stormwater Treatment Area, south Florida (USA). These cells include an emergent aquatic vegetation cell dominated by Typha spp.(cattail) and a submerged aquatic vegetation cell composed of species such as Chara spp. (muskgrass) and Potamgeton spp. (pondweed). Unlike results of prior studies, this study demonstrated that C, N, and P stoichiometry can be highly variable within and between wetland ecosystem compartments in a P-limited ecosystem. Generally, total P declined along the flow path in all ecosystem compartments, whereas trends in total N and C were not consistent. Meanwhile, TN:TP relationships increased as C:N and C:P varied in various compartments along the treatment flow paths. Assessment of wetland nutrient stoichiometry between and within ecosystem compartments suggest decoupling of organic matter decomposition from nutrient mineralization which may have significant influences on nutrient removal rates and contrasting dominate vegetation communities. This information could be used to further understand water treatment performance of these constructed wetlands.Background Evaluation of carbon (C), nitrogen (N) and phosphorus (P) ratios in aquatic and terrestrial ecosystems can advance our understanding of biological processes, nutrient cycling and the fate of organic matter (OM) in aquatic ecosystems. Eutrophication of aquatic ecosystems can disrupt the accumulation and decomposition of OM which serves as the base of the aquatic food web, and is central to the effectiveness of a treatment wetland. This study investigated nutrient stoichiometry within and between wetland ecosystem compartments (i.e. water column, vegetation, flocculent and soil) of two treatment flow-ways (FWs) in the Everglades Stormwater Treatment Areas located in south Florida (USA). These FWs include an emergent aquatic vegetation cell dominated by Typha spp.(cattail) and a submerged aquatic vegetation cell composed of species such as Chara spp. (muskgrass) and Potamogeton spp. (pondweed). The primary objective of this evaluation was to determine if nutrient stoichiometry is consistent within and between ecosystems and compartments to understand biogeochemical cycling and controls of nutrient removal within a treatment wetland ecosystem. Results This study demonstrates that C, N, and P stoichiometry can be highly variable among ecosystem compartments and between differing wetland ecosystems. Generally, total P declined along the length of each treatment FW in all ecosystem compartments, whereas trends in total N and C trends were more variable. These changes in C and nutrient concentrations result in variable nutrient stoichiometry along treatment FWs signaling potential changes in absolute and relative nutrient availability and biogeochemical processes. Conclusions Assessment of wetland nutrient stoichiometry between and within ecosystem compartments suggest decoupling of C:N:P relationships likely as a consequence of differential external nutrient supply, differences in primary producer communities and differential decomposition of organic matter. However, stoichiometry varies often monotonous along the flow paths, likely exhibiting a response to nutrient loading. Differences in C:N:P ratios in primary producers, light availability, microbial immobilization in the early stage of decomposition as well as nutrient mining during decomposition of OM are likely feedback mechanisms that lead to deviations from fixed stoichiometry, which in turn may have considerable influence on nutrient removal rates. This information could be used to further understand water treatment performance with respect to stoichiometric processes and OM decomposition.

Response to Julian et al. (2015) “Comment on and Reinterpretation of Gabriel et al. (2014) ‘Fish Mercury and Surface Water Sulfate Relationships in the Everglades Protection Area’”

AbstractThe purpose of this forum is to respond to a rebuttal submitted by Julian et al., Environ Manag 55:1–5, 2015 where they outlined their overall disagreement with the data preparation, methods, and interpretation of results presented in Gabriel et al. (Environ Manag 53:583–593, 2014). Here, we provide background information on the research premise presented in Gabriel et al. (Environ Manag 53:583–593, 2014) and provide a defense for this work using five themes. In spite of what Julian et al. perceive as limitations in the sampling methods and analytical tools used for this work, the relationships found between fish total mercury and surface water sulfate concentrations in Gabriel et al. (Environ Manag 53:583–593, 2014) are comparable to relationships between pore water methylmercury (MeHg) and pore water sulfate found in past studies indicating that sulfate is important to MeHg production and bioaccumulation in the Everglades. Julian et al. state “…there is no way to justify any ecosystem-wide sulfur strategy as a management approach to reduce mercury risk in the (Everglades) as suggested by Gabriel et al. (Environ Manag 53:583–593, 2014), Corrales et al. (Sci Tot Environ 409:2156–2162, 2011) and Orem et al. (Rev Environ Sci Technol 41 (S1):249–288, 2011).” We disagree, and having stated why sulfate input reduction to the Everglades may be the most effective means of reducing mercury in Everglades fish, it is important that research on sulfur and mercury biogeochemistry continues. If further studies support the relationship between sulfate loading reduction and MeHg reduction, sulfur mass balance studies should commence to (1) better quantify agricultural and connate seawater sulfate inputs and (2) define opportunities to reduce sulfate inputs to the Everglades ecosystem.