Water Column Productivity, Calcite Precipitation, and Phosphorus Dynamics in Freshwater Marshes

Algal photosynthesis and respiration can cause significant diurnal changes in water chemistry, and can increase pH enough to cause precipitation of calcium carbonate minerals. During the precipitation of calcite (CaCO3) other chemical species such as phosphorus (P) can sorb onto the newly forming crystals and thus be removed from thewater column. While calcite precipitation and subsequent P removal have been studied extensively in lakes, rivers, and streams, they have not been studied in temperate wetlands. Calcite precipitation and associated P removal were examined in two full-scale 1-ha created experimental freshwater marshes and in twenty 1-m2 experimental mesocosms in central Ohio. Water, algae, and sediment samples were taken from July 1998 to May 1999 at sitesfrom the inflow to the outflow of the marshes. Diurnal dissolved oxygen data taken every half-hour from July 1996 through December 1998 at the experimental marshes were used to estimate gross primary production (GPP), respiration (R), and net primary production (NPP). NPP, GPP and R showed strong seasonal changes, with maxima in the summer (3.43 to 6.23 g O2 m-2 d-1) and minima (0.36 to 2.10 g O2 m-2 d-1) in the winter. SummerGPP values were similar to values for eutrophic hardwater lakes, indicating that the shallow euphotic zone of wetlands can be as productive on an areal basis as deeper euphotic zones in lakes. Summer GPP values in the middle subbasins were not significantly different between the planted and unplanted wetland in 1996 or 1998, butwere significantly higher in the planted wetland in 1997. Conductivity and temperature data were used in conjunction with hydrologic data to develop budgets for total dissolved solids (TDS). Retention of total dissolved solids ranged from -0.7 to 12.7 Mg ha-1 yr-1 (-0.4 to 13.5 percent retention, respectively) and averaged 7.9 Mg ha-1 yr-1 (6.3 percent retention). The two wetlands were not significantly different in total or percent retention from 1996 to 1998; however, Wetland 2 had higher total and percent retention in 1996 and 1997, while Wetland 1 had higher total and percent retention in 1998.The total dissolved solids budget showed that the wetland acted as sinks for dissolved materials, consistent with calcite precipitation. Calcite saturation indices were positive for all water samples, indicating that calcite precipitation is thermodynamically favored. Ca and P concentrations decreased from inflow to outflow, and calcite and dolomite were found in the algal biomass, as well as in the wetland sediments, while suspended sediment samples from the river inflow did not contain significant amounts of calcite, indicating that the calcite precipitated in the wetlands and was not imported as suspended riverine sediments. Dolomite may have been imported via the river inflow. Total calcite in both basin sediments increased by an estimated 4.5 metric tons ha-1 yr-1 and and dolomite by over 1.4 metric tons ha-1 yr-1 from 1994 to 1999. Scanning electron microscopy showed calcareous material encrusting algal filaments. The total amount of P associated with calcite was up to 47 percent of the total P contained in the algal mat, suggesting that P coprecipitation essentially doubled the P removal capability of the algal mat.Calcite precipitation was also investigated in twenty 380-L shallow-water (30 cm) mesocosms to determine whether calcite precipitation/dissolution occurred on a diurnal time-scale in wetlands, and whether sorption with calcite was a significant sink for P. Ten mesocosms were covered with black cloth to inhibit photosynthesis, while ten mesocosmswere left uncovered and stocked with filamentous algae from the experimental marshes (major spp. Cladophora, Rhizoclonium, Hydrodictyon). Water, algal biomass and sediment samples were taken from June 1998 to May 1999. Saturation index values were always positive, showing that calcite precipitation was thermodynamically favored for both treatments on all sampling dates. Dissolved oxygen, temperature, pH, and saturation index showed strong diurnal patterns in the uncovered mesocosms, and less so in the covered mesocosms. Calcium, soluble reactive P, and total P showed no diurnal changes in either treatment, but were significantly lower in the water column of the uncovered mesocosms. Calcite precipitation occurred in the algal mats of the uncovered mesocosms, and calcite inthe algal mats increased by 6.55 ± 1.05 g-eq CaCO3 in the uncovered mesocosms over one growing season. There were no algal mats present in the covered mesocosms, and calcite and dolomite in all mesocosm sediments were not significantly different from the initial soil samples.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Environmental Science

Grantor dc:publisher

The Ohio State University

Year dc:date

2000

Author dc:creator

• Liptak, Michael A.

Contributors dc:contributor

• J. Mitsch, William

• Environmental Science

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1364288585

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1364288585