Potential export of soluble reactive phosphorus from a coastal wetland in a cold-temperate lagoon system: Buffer capacities of macrophytes and impact on phytoplankton

Abstract

The main pathways for phosphorus flux from land to sea are particle-associated (erosion) and dissolved runoff (rivers, groundwater, and agricultural drainage systems). These pathways can act as diffused sources for aquatic systems and support primary production, therefore, counteracting the efforts aimed at reducing phosphorus input from point sources such as sewage treatment plants. Phosphorus supports primary production in the water column and can elevate phytoplankton and macrophyte growth. Coastal wetlands with emerged (Phragmites australis) and submerged (Stuckenia pectinata and Chara sp.) macrophytes can affect phosphorus fluxes in the land-water transitional zone. The macrophytes have the potential to act as a buffer for phosphorus run-off. The aim of this study was to determine the phosphorus stocks in the transitional land-sea zone of a cold temperate lagoon at the southern Baltic Sea. Phosphorus in macrophytes, water samples, and phytoplankton growth were analyzed along a gradient moving away from the wetland. The phosphorus stocks in the above ground biomass of the Phragmites plants were the highest at the end of August and with more than 8000mgPm in the interior zone of the wetland, threefold the amount of P in Phragmites plant tissue at the wetland fringe. The submerged macrophytes stored only 300mgPm, close to the wetland. Concentrations of soluble reactive phosphorus in the water column were higher in the zones of emerged macrophytes than in the zones of submerged macrophytes and decreased along the land-sea transect. Phytoplankton could grow proximal to the wetland during all seasons, but not further away. This study indicates that macrophytes can act as phosphorus sinks. However, short-term releases of phosphate within the Phragmites wetland have the potential to lead to phytoplankton growth. Phytoplankton can use these nutrient pulses either immediately or later, and support high biomass and turbidity within the system.

Effects of Water Depth and Phosphorus Availability on Nitrogen Removal in Agricultural Wetlands

“…The effects of P addition confirm previous studies that have reported that denitrification rate is correlated to the P availability, as a higher P availability can positively affect microbial denitrification [44,46]. Furthermore, increased plant production due to P additions also could have contributed to N removal through increased plant uptake of N as well as by providing organic carbon or surface areas to denitrifying bacteria [14,35].…”

“…These divergent conclusions about the effects of vegetation complicate our understanding of the effects of water depth on N removal in FWS wetlands. Phosphorus (P) is a key limiting nutrient that can influence the growth of macrophytes [44,45]. An increased growth of macrophytes, due to a higher P availability, may therefore result in an increased uptake of N by transforming into biomass, or it may indirectly promote denitrification by providing organic carbon or suitable surfaces for bacteria.…”

Magnitude and influence of atmospheric phosphorus deposition on the southern Baltic Sea coast over 23 years: implications for coastal waters

“…There are currently no reliable data on the magnitude of such events. Nonetheless, phytoplankton was described to grow all year round along the land-water contact zone within this ecosystem [41].…”

“…Bulk deposition of P by dust and rain fertilizes phytoplankton in the euphotic and entire zone of a water body, in contrast to other patchy distributed P sources, like resuspension from sediment [42], or across the landwater transitional zone [41].…”

Dynamics of primary productivity in relation to submerged vegetation of a shallow, eutrophic lagoon: a field and mesocosm study

“…Furthermore, phytoplankton grew throughout the year in the shallow areas in proximity to the reed belt and possible P runoff of the DZLS, whereas there was only minor growth in deeper lagoon parts [11]. P stocks in the sediment were described to be highest in shallow areas [50], probably caused by large macrozoobenthos populations [60] who may increase nutrient burial through two-to three-fold increased sediment-water contact zones [61].…”