DOI: 10.5061/dryad.c2722m0
title: Data from: A novel approach to determining dynamic nitrogen thresholds for seagrass conservation

description: 1. Seagrass decline is often related to eutrophication, with sudden and
 drastic losses attributed to tipping points in nutrient loads. The
 identification of these threshold loads is an important step in the
 sustainable management of nutrient discharges. 2. In this study, a novel
 methodological approach is presented to simulate the spatial and temporal
 dynamics of coastal nitrogen loads, and its relationship to seagrass loss.
 The analysis allows the identification of nitrogen thresholds associated
 with the loss of Posidonia and Amphibolis spp. in Adelaide, South
 Australia. 3. The identified thresholds varied between 0.8 and 1.1 t N
 km-2 over 6 months, and explained up to 95% of all seagrass losses in the
 region. 4. Posidonia spp. was predominantly lost nearshore, indicating a
 threshold for this species in the higher end of the values reported here.
 In contrast, Amphibolis spp. was selectively lost further offshore,
 suggesting a lower threshold for the onset of fragmentation and decline.
 5. Nitrogen pressure was concentrated over the wetter months of the year
 between late autumn and early spring. Pulsed pressure peaking in August
 likely affected thresholds by reducing resilience in the system. 6.
 Synthesis and applications. This study derives, for the first time,
 nitrogen load thresholds for the loss of the seagrasses Posidonia and
 Amphibolis spp., highlighting the low tolerance of these keystone
 temperate species to nitrogen pressure. The methodology developed as part
 of the work provides a tool to inform planning and improved management of
 nutrient discharges from land to facilitate seagrass conservation.
description: Nitrogen
 loadsDaily nitrogen loads
 from rivers, industry and wastewater treatment plants discharging to the
 Adelaide coast in 1975, including coordinates. Loads calculated from data
 compiled during the Adelaide Coastal Waters Study and published by
 Wilkinson, J., White, N., Smythe, L., Hutson, J., Bestland, E., Simmons,
 C., Lamontagne, S. & Fallowfield, H. (2005) Volumes of inputs, their
 concentrations and loads received by Adelaide metropolitan coastal waters.
 ACWS Technical Report No. 18 prepared for the Adelaide Coastal Waters
 Study Steering Committee. pp. 83. Flinders Centre for Coastal and
 Catchment Environments (Flinders University of SA), Adelaide, South
 Australia.loads.xlsxSeagrass extentGIS file showing seagrass cover in Adelaide in 1977 according to Hart, D. (1997) Near-shore seagrass change between 1949 and 1996 mapped using digital aerial orthophotography, metropolitan Adelaide area, Largs Bay-Aldinga, South Australia. A report prepared for the South Australian EPA. pp. 12. Department of Environment and Natural Resources, Adelaide, South Australia.Seagrass_extent.zipSeagrass LossGIS file showing seagrass loss in Adelaide between 1970 and 1977 according to Hart, D. (1997) Near-shore seagrass change between 1949 and 1996 mapped using digital aerial orthophotography, metropolitan Adelaide area, Largs Bay-Aldinga, South Australia. A report prepared for the South Australian EPA. pp. 12. Department of Environment and Natural Resources, Adelaide, South Australia.Seagrass_Loss.zipASL codeComputer code to calculate area specific loads in coastal areas.