Influence of Vegetation on Long-term Phosphorus Sequestration in Subtropical Treatment Wetlands.

Sustainable operation of a treatment wetland depends on its continued treatment of influent water to achieve desired outflow water quality targets. Water treatment or nutrient reduction is attained by a combination of biotic and abiotic processes. We studied one of the world's largest treatment wetlands established to revive the Florida Everglades from impacts of excessive phosphorus (P) inputs. Phosphorus retained in the treatment wetlands is sequestered within the accumulated material via biotic and abiotic pathways that are influenced by the existing wetland vegetation. Recently accreted soils (RAS) provide a major sink for stored P, and long-term P removal efficiency of treatment wetlands is governed by the stability of accreted P because more stable P pools are less susceptible to mobilization and loss. We quantified reactive P (extracted with acid and alkali) and nonreactive P (not extracted with acid and alkali) pools in wetland soils by using an operationally defined P fractionation scheme and assessed the effect of emergent vs. submerged vegetation communities on stability of sequestered P. Reactive P comprised 63 to 79% of total P in wetland soils without a clear difference between two vegetation groups. The quantities of reactive P forms (inorganic vs. organic P) were significantly different between two vegetation types. A higher proportion of reactive P was stored as organic P in flocculent detrital organic matter (floc) and RAS under emergent vegetation (46-47% total P) in comparison with submerged vegetation (21-34% total P). The dominant P removal pathway in the submerged vegetation system was associated with calcium whereas plant uptake and peat burial appeared to be the main pathway in the emergent vegetation system.

Impacts of land use on Indian mangrove forest carbon stocks: Implications for conservation and management.

Globally, mangrove forests represents only 0.7% of world's tropical forested area but are highly threatened due to susceptibility to climate change, sea level rise, and increasing pressures from human population growth in coastal regions. Our study was carried out in the Bhitarkanika Conservation Area (BCA), the second-largest mangrove area in eastern India. We assessed total ecosystem carbon (C) stocks at four land use types representing varying degree of disturbances. Ranked in order of increasing impacts, these sites included dense mangrove forests, scrub mangroves, restored/planted mangroves, and abandoned aquaculture ponds. These impacts include both natural and/or anthropogenic disturbances causing stress, degradation, and destruction of mangroves. Mean vegetation C stocks (including both above- and belowground pools; mean ± standard error) in aquaculture, planted, scrub, and dense mangroves were 0, 7 ± 4, 65 ± 11 and 100 ± 11 Mg C/ha, respectively. Average soil C pools for aquaculture, planted, scrub, and dense mangroves were 61 ± 8, 92 ± 20, 177 ± 14, and 134 ± 17 Mg C/ha, respectively. Mangrove soils constituted largest fraction of total ecosystem C stocks at all sampled sites (aquaculture [100%], planted [90%], scrub [72%], and dense mangrove [57%]). Within BCA, the four studied land use types covered an area of ~167 km2 and the total ecosystem C stocks were 0.07 Tg C for aquaculture (~12 km2 ), 0.25 Tg C for planted/ restored mangrove (~24 km2 ), 2.29 teragrams (Tg) Tg C for scrub (~93 km2 ), and 0.89 Tg C for dense mangroves (~38 km2 ). Although BCA is protected under Indian wildlife protection and conservation laws, ~150 000 people inhabit this area and are directly or indirectly dependent on mangrove resources for sustenance. Estimates of C stocks of Bhitarkanika mangroves and recognition of their role as a C repository could provide an additional reason to support conservation and restoration of Bhitarkanika mangroves. Harvesting or destructive exploitation of mangroves by local communities for economic gains can potentially be minimized by enabling these communities to avail themselves of carbon offset/conservation payments under approved climate change mitigation strategies and actions.

Soil and phosphorus accretion rates in sub-tropical wetlands: Everglades Stormwater Treatment Areas as a case example.

Wetlands are known to serve as sinks for particulate matter and associated nutrients and contaminants. Consequently rate of soil accretion is critical for continued performance of wetlands to provide ecosystem services including water quality improvement and reduce excess contaminant loads into downstream waters. Here we demonstrate a new technique to determine rate of soil accretion in selected subtropical treatment wetlands located in southern USA. We also report changes in soil accretion rates and subsequent phosphorus (P) removal efficiency with increasing operational history of these treatment wetlands. Utilizing discernible signatures preserved within the soil depth profiles, 'change points' (CP) that corresponded to specific events in the life history of a wetland were determined. The CP was observed as an abrupt transition in the physico-chemical properties of soil as a manifestation of prevailing historical conditions (e.g. startup of treatment wetlands in this case). Vertical depth of CP from the soil surface was equivalent to the depth of recently accreted soil (RAS) and used for soil accretion rate calculations. Annual soil and P accretion rates determined using CP technique (CPT) in studied wetlands ranged from 1.0±0.3 to 1.7±0.8 cm yr(-1) and 1.3±0.6 to 3.3±2 g m(-2) yr(-1), respectively. There was no difference in RAS depth between emergent and submerged aquatic vegetation communities found at the study location. Our results showed that soil and P accretion rates leveled off after 10 yr of treatment wetlands' operation. On comparison, soil accretion rates and RAS depth determined by CPT were commensurate with that measured by other techniques. CPT can be easily used where a reliable record of wetland establishment date or some significant alteration/perturbation is available. This technique offers a relatively simple alternative to determine vertical accretion rates in free-water surface wetlands.