Effects of Nutrient Nonpoint Source Pollution on Seagrasses

in Redfish Bay

Kelly Darnell

GISWR Fall 2009

Eutrophication• Increase in nutrient concentration• Coastal eutrophication increasing

– Anthropogenic impacts: nutrient nonpoint source (NPS) pollution

• Negative effects on coastal organisms, systems– Decreased light irradiance, hypoxia, anoxia, decreased

water quality, stress species

www.marietta.edu

Seagrasses

• Submerged marine plants• Ecosystem services

– Sediment stabilization, particle settlement, food, habitat, nursery proper ecosystem functioning

• High light requirements make seagrasses sensitive to decreased water quality

• Declining worldwide, TX– Anthropogenic impacts

www.dep.state.fl.us

www.unep-wcmc.org

Seagrass Monitoring in Texas

• Dunton et al. (2005)– Monitoring program for seagrass health indicators

in Redfish Bay– Abiotic: water column nutrients, chlorophyll a,

total suspended solids (TSS), sediment nutrients– Biotic: seagrass cover, biomass, morphology

• Suggest input of nutrient NPS pollution– Water column nutrients

Objectives

• Obtain a visual representation of suggested nutrient NPS pollution in Redfish Bay– Better understanding of NPS pollution inputs– Cascading effects on seagrasses

• Water column, sediment and seagrass nutrients, seagrass morphology – Dunton et al. (2005)

Monitoring Sites: Redfish Bay, TX

• 30 sites• 2002-2005

– Summer data

Site 1

Site 30

Phosphate (PO4): 2002-2005

• No clear trends

Nitrate (NO3): 2002-2005

• No clear trends

• Water column nutrients spatially and temporally variable

• Suggested nutrient NPS input in 2002

Phosphate and Nitrate:

Water Column and Sediment Quality: 2002

1 6 11 16 21 260

5

10

15

20

25

30

f(x) = − 0.406155011278117 x + 14.0241711805539R² = 0.353337877988408

Total Suspended Solids by Site

Site

Tota

l Sus

pend

ed S

olid

Con

cent

ratio

n

1 6 11 16 21 260

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

f(x) = − 0.0231794586577679 x + 1.12311494252874R² = 0.220541742418652

Average Porewater Ammonium by Site

Site

Aver

age

Pore

wat

er N

H4 (u

M)

• TSS and average porewater NH4 higher in Northern part of Bay– TSS possibly

detrimental to seagrasses

– NH4 stimulate seagrass growth

Seagrass Parameters:

2002

• Dominant seagrass• Turtlegrass leaf

length and aboveground biomass slightly lower in Northern part of Bay– Seagrass may be

stressed

1 6 11 16 21 2605

101520253035404550

f(x) = 0.328351540088667 x + 24.9238567413289R² = 0.221138839726108

Average Turtlegrass Leaf Length

Site

Leaf

Leng

th (c

m)

1 6 11 16 21 260

50

100

150

200

250

300

350

f(x) = 2.60579688103101 x + 133.345673781427R² = 0.0516306401020048

Average Turtlegrass Aboveground Biomass

Site

Abov

egro

und

Biom

ass (

g DW

m−2

)

Conclusions So Far

• Results support existence of nutrient NPS pollution in Redfish Bay

• Results suggest seagrass may be negatively affected by indicated NPS pollution

Future Plans

• Compare nutrient inputs to local precipitation– Obtain an indication of runoff

• Visually represent:– Water column nutrient concentrations by site– Seagrass leaf nutrients by site and year– Seagrass above- and below-ground biomass

by site and year

Questions?

Sources

• Dunton KH, Kopecky AL, Maidment D (2005) Monitoring design criteria and biological indicators for seagrass conservation in Texas coastal waters. Final Report for Regional Environmental Monitoring and Assessment Program, EPA

• Texas World Imagery Basemap obtained from ESRI (resources.esri.com)