Thomas W. Dreschel

Effects of plant community and phosphorus loading rate on constructed wetland performance in Florida, USA

We evaluated the effectiveness of constructed wetlands with varying plant communities for phosphorus (P) reduction from the Everglades Agricultural Area runoff in south Florida. Weekly or biweekly water samples from the inflow and outflow regions of 11 test cells (2,000 m2) were analyzed for various forms of P and other selected water quality variables between January 2002 and August 2004. Test cells located at the north site received water with a high average total P (TP) concentration (72 μg L−1), while test cells located at the south site received water with a lower average TP concentration (43 μg L−1). These test cells were dominated by an emergent vascular plant-cattail (Typha latifolia), submerged aquatic vegetation or SAV (Najas guadalupensis, Chara sp., Ceratophyllum demersum, and Hydrilla verticillata), or algal periphyton (mixed with Eleocharis cellulosa and Utricularia spp. in the south site only). Under a constant hydraulic loading rate (9.27 m yr−1), these test cells removed P effectively, with removal efficiencies of 56%–65% at the north site and 35%–62% at the south site. The mass removal rate and rate constant at the north site were also higher than at the south site. Soluble reactive P (SRP) and particulate P were the major forms at inflow and were removed effectively by all of the test cells. The removal of dissolved organic P was significant (∼60%) in the cattail and periphyton test cells, but no removal was detected in the SAV test cells. At the north site, P removal efficiency of the cattail test cells was slightly higher than that of the SAV test cells. At the south site, periphyton test cells were the best performers. The removal of SRP was positively correlated with the removal of calcium in the majority of the test cells, pointing to the potential importance of co-precipitation of calcium carbonate and SRP. Direct plant uptake, wetland filtering, microbial degradation, and co-precipitation with calcium carbonate were mechanisms thought to be responsible for P removal in these wetlands. Outflow TP concentration, an important measure for restoration performance, increased continuously with the increases in the TP mass loading rate at the north site, but peaked at approximately 30 μg L−1 when the TP mass loading rate reached 0.5 g m−2 yr−1 at the south site.

Trees: a powerful geomorphic agent governing the landscape evolution of a subtropical wetland

Transpiration-driven ion accumulation in soil has been invoked as a biological and physical feedback mechanism in wetlands that governs topographic differences by regulating soil accretion—with greater transpiration, ion accumulation and soil accretion occurring on tree islands as compared to the surrounding marsh. The strength of this mechanism is hypothesized to be controlled by the ratio of evapotranspiration (ET) to precipitation (P), where under greater ET to P conditions soil accretion may move from organic to mineral in nature. We tested the existence of this mechanism on tree islands in a subtropical wetland, determined if it supports mineral soil formation, and assessed its control on the development of nutrient resource contrasts (tree islands–marsh). To test our hypotheses, biannual measurements of groundwater, surface water and aboveground biomass were made from 2007 to 2012. Water samples were analyzed for water isotopes, concentrations of major ions, and total and dissolved nutrients on constructed tree islands. We found that tree transpiration led to the advective movement of water and associated ions toward the center of the tree islands, supporting CaCO3 precipitation. CaCO3 accretion on the tree islands was estimated at roughly 1xa0mm per decade, and represented 5xa0% of the total soil accretion since the islands’ planting. We also observed depletion in groundwater nutrient concentrations as tree biomass accumulated, indicative of tight nutrient cycling. This work provides direct evidence that trees can act as powerful geomorphic agents in wetland systems, forming mineral soils that support landscape heterogeneity on time scales of centuries to millennia.

Investigation of long-term trends in selected physical and chemical parameters of inflows to Everglades National Park, 1977-2005

Data of seven water-quality parameters from inflows to the Everglades National Park were collected at three monitoring stations and analyzed for temporal trends. The best-fit models for the existence of trends were evaluated. The Kolmogorov–Smirnov test was used to select the theoretical distribution which best fit the data. Simple regression was used to examine the parameters for concentration–discharge relationships. The power and linear models were found to better describe the concentration–discharge relationships. Loess trend lines indicated a similar trend period of color value change during the selected period at three stations. The sharp decrease in color after 1990 at each station is consistent with the beneficial impacts of control measures, which include Best Management Practices implementation in the Everglades Agricultural Area, water management improvement, and the construction of additional stormwater treatment areas. The existence of trend analysis was performed by using the uncensored seasonal Kendall test. Conductivity and color decreased significantly at two (S12A and S333) of three stations. Alkalinity decreased significantly at S333. A “best-fit” model was selected to describe a trend change with statistical significance; the second-order equation provides a better description of the trend. This study also indicates that by using the routinely measured water-quality parameters, it may be easier to quantify the changes in water quality to aid in making water resources management decisions.

A Simple Planting Technique for Re-establishing Trees Where Frequent Inundation Occurs

Many of the Everglades tree islands have lost elevation over the past century and most of their trees have died such that they are now covered with herbaceous plants. This protocol describes a simple, cost-effective tree planting technique needed for restoring degraded Everglade tree islands. The design is patterned after a natural Everglades process that creates floating peat islands, which allows tree survival and growth in flooded conditions and often leads to the development of tree islands. Commercially available peat bags were used as the medium for the growth and establishment of potted native tree saplings. The pop-up configuration floated initially and provided additional elevation to minimize inundation, with a single native tree species sapling and a single tree fertilizer spike. During a 3 year study involving 105 pop-ups, most plants survived (80%) and many thrived. Determining whether this technique can establish trees on a degraded tree island will require longer studies and extensive field tests.