Interannual Improvement in Sea Lettuce Blooms in an Agricultural Catchment

Abstract

Riverine nutrient loading from agriculture is one of the most prominent pressures in the second cycle of river basin management planning for the European Union (EU) Water Framework Directive (WFD). Better farmyard nutrient management planning is the measure most likely to reduce agricultural nutrient loading to catchment watercourses and coastal receiving waters. The adjoining Argideen Estuary and Courtmacsherry Bay in the south west of Ireland drain a 150 km 2 catchment comprising mainly agricultural land. The receiving waters were allocated Poor ecological status under the WFD at the most recent appraisal. Sub-hourly water quality monitoring in the Timoleague River has been carried out by the Teagasc Agricultural Catchments Program to track the changes in nutrient loading to the Argideen Estuary in response to improved farming practice. A bio-physical model of the adjoining Argideen Estuary and Courtmacsherry Bay was calibrated subject to the prevailing climatic and nutrient loading regime. Six nutrient load scenarios were simulated to determine their impact upon macroalgae and phytoplankton bloom magnitude. In addition, nutrient flow-load relationships were derived for summers 2010 and 2016 to elucidate the improvements induced by better catchment management practice. Flow-load relationships for dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) for each year were applied to the flow data for the other year, to query the outcome if (1) there had been no change in farm management practice between 2010 and 2016, or (2) the improved farm management practice in place by 2016 had been implemented by 2010. The difference between expediting and delaying improvement in farm nutrient management practice was a 5% increase in DIN loading and a 233% increase in DIP load. Application of this higher estimated load to the calibrated bio-physical model projected an increase in 2016 Ulva bloom magnitude from 381t to 1,391t. Although phosphorus retention within the catchment has improved in recent years, with an attendant improvement in Ulva bloom magnitudes, flow connectivity in the catchment still facilitates a higher phosphorus transfer during large rainfall events. A high amount of phosphorus is stored within the catchment, while point source pressures continue to contribute to phosphorus transfer to streams during periods of low flow.

Internal Nutrient Loading Controls Macroalgal and Cyanobacterial Succession in a Coastal Lagoon Restored by Managed Realignment of Agricultural Land

“…Drifting clusters of F. vesiculosus has been observed frequently along Danish coasts (Valdemarsen et al, 2010;Canal-Vergés et al, 2014), and the drifting form without holdfast and typical air vesicles at Gyldensteen Coastal Lagoon is similar to that reported from the Wadden Sea (Albrecht, 1998). Both F. vesiculosus and A. vermiculophylla are associated with nutrient poor environments (Wikström et al, 2016), while fast growing opportunistic green and brown species are indicative of eutrophic conditions (McGovern et al, 2019). The gradual shift from opportunistic to perennial macroalgal species in Gyldensteen Coastal Lagoon therefore conforms with recognized ecological succession patterns (Sousa, 1979;Valiela, 1984), and implies that this newly flooded environment progresses toward an improved ecological status within a period of 5 years (Wells et al, 2007).…”

Assessing the Impact of Physical and Anthropogenic Environmental Factors in Determining the Habitat Suitability of Seagrass Ecosystems

“…The role of anthropogenic factors has also been suggested to be equally important in determining geographic distributions by limiting resources through eutrophication, smothering of sediment, and physical disturbance and mortality [15,45,46]; however, many SDM studies often exclude or neglect these variables during model parameterisation, or recommend their inclusion in future research [47,48]. For example, agricultural run-off into river catchments causes eutrophication in the form of Ulva blooms [49], which then subsequently decompose releasing hydrogen sulfide into the water, negatively impacting intertidal seagrasses [50]. Subsequently, distribution models could be improved by explicitly incorporating such anthropogenic drivers; however, to-date anthropogenic factors have seldom been incorporated in parameterizing seagrass distributions, meaning there remains a need to investigate the importance of these factors on determining the geographic distribution of seagrass species.…”