Susan Newman

Extraction of soil organic phosphorus.

Organic phosphorus is an important component of soil biogeochemical cycles, but must be extracted from soil prior to analysis. Here we critically review the extraction of soil organic phosphorus, including procedures for quantification, speciation, and assessment of biological availability. Quantitative extraction conventionally requires strong acids and bases, which inevitably alter chemical structure. However, a single-step procedure involving sodium hydroxide and EDTA (ethylenediaminetetraacetate) is suitable for most soils and facilitates subsequent speciation by nuclear magnetic resonance spectroscopy. Analysis of extracts by molybdate colorimetry is a potential source of error in all procedures, because organic phosphorus is overestimated in the presence of inorganic polyphosphates or complexes between inorganic phosphate and humic substances. Sequential extraction schemes fractionate organic phosphorus based on chemical solubility, but the link to potential bioavailability is misleading. Research should be directed urgently towards establishing extractable pools of soil organic phosphorus with ecological relevance.

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...

FACTORS INFLUENCING CATTAIL ABUNDANCE IN THE NORTHERN EVERGLADES

Since the early 1900s, the Everglades have been influenced by anthropogenic actions including altered hydrology and increased nutrient loading. In the northern Everglades an apparent effect of . these disturbances has been the development and proliferation of dense cattail Typha spp. stands

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.

Maintaining tree islands in the Florida Everglades: nutrient redistribution is the key

The Florida Everglades is an oligotrophic wetland system with tree islands as one of its most prominent landscape features. Total soil phosphorus concentrations on tree islands can be 6 to 100 times greater than phosphorus levels in the surrounding marshes and sloughs, making tree islands nutrient hotspots. Several mechanisms are believed to redistribute phosphorus to tree islands: subsurface water flows generated by evapotranspiration of trees, higher deposition rates of dry fallout, deposition of guano by birds and other animals, groundwater upwelling, and bedrock mineralization by tree exudates. A conceptual model is proposed, in which the focused redistribution of limiting nutrients, especially phosphorus, onto tree islands controls their maintenance and expansion. Because of increased primary production and peat accretion rates, the redistribution of phosphorus can result in an increase in both tree island elevation and size. Human changes to hydrology have greatly decreased the number and size of tr...

Decomposition responses to phosphorus enrichment in an Everglades (USA) slough

The effects of phosphorus (P) enrichment ondecomposition rates were measured in a Ploading experiment conducted in an oligotrophicmarsh in the northern Everglades, USA. In thisstudy, eighteen 2.5 m2 enclosures(mesocosms) were placed in a pristineopen-water (slough) wetland and subjectedweekly to 6 inorganic P loads; 0, 0.2, 0.4,0.8, 1.6 and 3.2 g·m−2g·yr−1. Phosphorus accumulated rapidly in the benthicperiphyton and unconsolidated detrital (benthicfloc) layer and significantly higher Pconcentrations were recorded after 1 yr of Paddition. In contrast, a significant increasein surface soil (0–3 cm) TP concentrations wasmeasured in the surface soil layer only after 3yr of loading at the highest dose. Plantlitter and benthic floc/soil decompositionrates were measured using litter bags,containing sawgrass (Cladium jamaicenseCrantz) leaves, and cotton (cellulose) strips,respectively. Litter bag weight losses weresimilar among treatments and averaged 30% atthe end of the 3 yr study period. Litter Nconcentrations increased over time by anaverage of 80% at P loads < 1.6g·m−2·yr−1, and by > 120% at Ploads ≥ 1.6 g·m−2·yr−1.In contrast,litter P concentrations declined up to 50% inthe first 6 months in all P loads and onlysubsequently increased in the two highestP-loaded mesocosms. Cotton strip decaydemonstrated that benthic floc and soilmicrobial activity increased within 5 mo of Paddition with more significant treatmenteffects in the benthic than the soil layer. The influence of soil microbial transformationswas shown in porewater chemistry changes. While porewater P levels remained close tobackground concentrations throughout the study,porewater NH4+ and Ca2+increased in response to P enrichment,suggesting that one significant effect of Penrichment in this oligotrophic peat system isenhanced nutrient regeneration.

MULTIPLE REGIME SHIFTS IN A SUBTROPICAL PEATLAND: COMMUNITY-SPECIFIC THRESHOLDS TO EUTROPHICATION

Ecosystems have a natural resilience to perturbations, where resilience is the magnitude of a disturbance that an ecosystem can resist before changes in structure, function, and services result in a regime shift. The Everglades region of Florida, USA, has been detrimentally impacted by phosphorus (P) enrichment and a regime shift from Cladium (sawgrass) to Typha (cattail) marsh has been described. We examine another facet of the low nutrient Everglades stability regime, open-water sloughs, to determine if eutrophication leads to similar regime shifts. We analyzed surface water P and soil P as controlling variables that, once a critical threshold is surpassed, alter ecosystem state variables. Nonlinear relationships between P and vegetation were observed along a northern Everglades eutrophication gradient. In addition to the Cladium-Typha regime shift, a second independent regime shift, slough-Typha, was identified. Synoptic surveys of 49 sloughs within the boundary between the slough and Typha regime revealed that surface water total phosphorus (TP) and the benthic algal floe layer (BAFL) were the controlling variables, with critical thresholds of 11 ug/L and 412 mg/kg, respectively. The slough regime below these thresholds was characterized by calcareous periphyton (BAFL TP = 298 mg P/kg; BAFL calcium = 149 g Ca/kg). Above the TP thresholds, vegetation composition shifted to open-marsh species with significantly higher BAFL TP (700 mg P/kg) and total organic carbon (TOC) (350 g C/kg). A second BAFL TP threshold occurred at 712 mg P/kg, above which Nymphaea dominated and BAFL TP (1034 mg P/kg) and TOC (417 g C/kg) significantly increased. Nymphaea sloughs transitioned to the Typha regime. The boundary reflects the loss of ecosystem resilience due to eutrophication. Both low-nutrient stability regimes (slough and Cladium) lie precariously close to the P critical threshold but differ in how eutrophication is absorbed and resisted. The slough regime transitions rapidly through a series of ecosystem state changes linked to positive feedback loops that affect P dynamics, whereas the Cladium regime does not. An adaptive management strategy has been implemented to address the surface water TP threshold; however, to ensure successful restoration of the Everglades, the BAFL and soil TP thresholds also need to be considered.

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.

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.

Heterogeneity of phosphorus distribution in a patterned landscape, the Florida Everglades

The biologically mediated transfer of nutrients from one part of a landscape to another may create nutrient gradients or subsidize the productivity at specific locations. If limited, this focused redistribution of the nutrient may create non-random landscape patterns that are unrelated to underlying environmental gradients. The Florida Everglades, USA, is a large freshwater wetland that is patterned with tree islands, elevated areas that support woody vegetation. A survey of 12 tree islands found total soil phosphorus levels 3–114 times greater on the island head than the surrounding marsh, indicating that the Florida Everglades is not a homogeneous oligotrophic system. It was estimated that historically 67% of the phosphorus entering the central Everglades was sequestered on tree islands, which are ~3.8% of the total land area. This internal redistribution of phosphorus onto tree islands due to the establishment of trees may be one reason that marshes have remained oligotrophic and may explain the spatial differentiation of the patterned Everglades landscape.