Identifying Zebra Mussel Distribution in the Hudson River Estuary Using High-Resolution Geophysical Data Angela L. Slagle*, W.B.F. Ryan, F.O. Nitsche, S.M. Carbotte, and R.E. Bell Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, USA * contact: [email protected]

ABSTRACT KINGSTON-SAUGERTIES AREA OTHER AREAS OF HUDSON RIVER ESTUARY Zebra mussels (Dreissena polymorpha), an invasive species, have fluorished In the Kingston-Saugerties stretch of the estuary, we use ArcGIS software Using ArcGIS Spatial Analyst, we can analyze all data types to determine The Hudson River Benthic Mapping Project includes geophysical and sediment and continue to spread in lakes and rivers of the northeast U.S. since their 1980s to create a Geographic Information System (GIS) that incorporates sidescan which parameters are most often associated with the presence of zebra sampling data for the entire Hudson River Estuary, from the New York Harbor to the introduction. Documented effects, including declining phyto- and zooplankton and sonar data and multibeam bathymetry with sediment samples, including grain mussels in this region of the estuary. We combine sediment type and Troy Dam. We find zebra mussels in most of the freshwater areas of the system. dissolved oxygen, increasing benthic primary production and water clarity, and size information and descriptive characteristics for each sample. GIS systems environment maps to generate polygon coverage of the area and overlay Although these areas have not yet been completely analyzed with respect to zebra damage to water intakes, reveal that this species plays an important role in offer many possibilities to display and compare data and provide a valuable point sample data, with zebra mussel presence/absence information for mussels, we have developed sediment type and environment maps and compared ecosystems. Studies show that zebra mussel distributions change through time, environment for detailed interpretation of our high-resolution data. We produce each point (Fig. 4, 5). We join this with sidescan sonar mosaics and visually with point samples. In the New Baltimore and Stockport Flats areas to the influenced by sediment properties as well as biological and chemical parameters. maps of sediment type by incorporating point samples and associated grain multibeam bathymetry maps. For each sample site, we now have information north, zebra mussel presence often coincides with areas of high sidescan backscatter In the Hudson River Estuary, a dataset including multibeam bathymetry, sidescan size information with sidescan sonar data (Fig. 1, 2). Using all available data, from all data types: presence/absence of zebra mussels, distance from shore, (Fig. 6, 7). Further south in Newburgh Bay, we find live zebra mussels on coarse sonar, subbottom profiles, and over 1,000 sediment cores and grabs, acquired we develop maps of process-based sedimentary environment, classifying the water depth, mean sidescan value for 20m radius around each point, deposits that may be associated with tributary input (Fig. 8) and in dynamic areas as part of the Hudson River Benthic Mapping Project funded by the New York estuary bottom as depositional, erosional/nondepositional, or dynamic (Fig. 3). dominant sediment type and sedimentary environment (Table 1). where we believe the estuary floor is influenced by the Newburgh-Beacon bridges (Fig. 9). State Dept. of Environmental Conservation, allows us to characterize existing zebra We use a similar method and ArcGIS analysis tools to investigate the mussel habitats. We identify zebra mussels from the northern extent of our study at distribution of zebra mussels in the Kingston-Saugerties area. Sample ID Zebra mussels Dist. to shore (m) Water depth (m) Mean sidescan Sed. Type Sed. Environment LW3-G31 0 343.13580515300 -6.30654001236 215.57099914551 muddy sand Dynamic - waves the Troy Dam south to Croton Point, where summer salinity range is 10-13 ppt. LW3-G32 0 437.85240295200 -10.68900012970 181.80099487305 sand Dynamic - waves 73°48'0"W 73°46'0"W 73°50'0"W 73°48'0"W 73°46'0"W LW3-G33 1 171.38350073100 -18.10519981384 171.66600036621 sand Dynamic - scour Zebra mussels primarily colonize coarse-grained substrates, but are rarely found in New Baltimore LW3-G34 1 84.64399342630 -18.82419967651 109.48600006104 muddy sand Dynamic - scour Stockport Flats depositional or dynamic areas where we find mobile sediment waves. We use our LW3-G35 1 401.55286750200 -15.47239971161 100.92099761963 gravelly sand Dynamic - debris LW3-G36 0 432.31422187100 -12.63389968872 135.91000366211 gravelly sand Dynamic - waves

42°34'0"N process-based analysis of the riverbed that incorporates geophysical data with LW3-G37 1 242.33025107400 -10.74740028381 150.84800720215 gravelly sand Dynamic - debris 42°34'0"N Sidescan Backscatter Table 1. Example showing the results of combining the point sample data and shoreline polygon (Fig. 4) with 42°22'0"N sediment samples and GIS software to map substrates threatened by future High 42°22'0"N sidescan sonar (Fig. 1), multibeam bathymetry, and sediment type and environment polygon data (Fig. 5). Each Low colonization, providing a useful tool for estuary managers. sample site is now associated with a specific set of attributes from all data types. 012

Kilometers Sidescan Backscatter LowHigh backscatter: 255 HIGH BACKSCATTER HighLow backscatter: 0 42°32'0"N 42°32'0"N 73°58'0"W 73°57'0"W 73°56'0"W 73°55'0"W 73°54'0"W 012 42°20'0"N 42°20'0"N 42°5'0"N 42°5'0"N Kilometers

Saugerties, NY HIGH BACKSCATTER Stockport Creek Castleton-on-Hudson ± Bridge

42°30'0"N Esopus Creek 42°18'0"N 42°4'0"N 42°30'0"N 42°18'0"N 42°4'0"N

Sidescan Backscatter s d

n

la

High Is

k

c

a

d o h Sample LW3-G33 c

S Low Zebra mussels 42°3'0"N 42°3'0"N 42°16'0"N Sample Sites 171 m from shore 42°16'0"N 42°28'0"N no zebra mussels 42°28'0"N = 18 m water depth Middle Ground Flats ++ Hudson, NY live zebra mussels Mean sidescan 172 New Baltimore, NY

Sand 73°48'0"W 73°46'0"W 73°50'0"W 73°48'0"W 73°46'0"W Dynamic scour 42°2'0"N Figure 6. Sidescan sonar mosaic of the New Baltimore Figure 7. Sidescan sonar mosaic of the Stockport Flats 42°2'0"N area in the northern estuary. Red circles indicate the area in the northern estuary. Red circles indicate the presence of live zebra mussels; gray circles indicate presence of live zebra mussels; gray circles indicate Sedimentary Environment their absence. Zebra mussels are commonly found in their absence. Zebra mussels are often found in areas Deposition - thick high backscatter areas, which may correspond to harder of high backscatter, specifically along the main channel Deposition - thin estuary floor, coarser grained deposits, or highly in this region. Tivoli Bay Tivoli Deposition - over bedrock 42°1'0"N 42°1'0"N Deposition - unres. thickness dynamic locations. Dynamic - waves Sample Sites Sediment Type Dynamic - drift no zebra mussels Dynamic - lineation live zebra mussels mud 74°W 73°58'0"W 74°2'0"W 74°W Dynamic - debris sandy mud 41°38'0"N 41°38'0"N Newburgh Bay, north Newburgh Bay, south gravelly mud Dynamic - scour 42°0'0"N Dynamic - slump 42°0'0"N muddy sand Sediment Type 41°32'0"N Sedimentary Environment 41°32'0"N mud Deposition - thick sand Dynamic - streaks sandy mud Deposition - thin gravelly sand Erosion - bedrock Combination of data types Deposition - over bedrock gravelly mud Deposition - unres. thickness muddy gravel Erosion - truncated Sample Sites muddy sand Dynamic - waves sand Dynamic - drift Newburgh-Beacon sandy gravel Erosion - non-deposition no zebra mussels Dynamic - lineation Bridges gravelly sand Dynamic - debris live zebra mussels gravel Unsurveyed muddy gravel Dynamic - scour sandy gravel Dynamic - slump 41°59'0"N Dynamic - streaks 41°59'0"N gravel Erosion - bedrock 41°36'0"N Figure 2. Sediment type interpretation for the Kingston Figure 3. Process-based sediment environment Figure 4. Grab sample sites in the Kingston-Saugerties Figure 5. Polygons resulting from the combination of 41°36'0"N Erosion - truncated 012 Erosion - non-deposition Marlboro, NY Unsurveyed to Saugerties, NY stretch, distinguished by combining interpretation of the Kingston-Saugerties area. We sorted area. Red circles indicate sites where live zebra sediment type and sedimentary environment data Kilometers 41°30'0"N 41°30'0"N

Kingston, NY grain size analyses from >150 grab samples and core the different processes into three major classes: mussels were found; gray circles, sites where live overlain with samples sites using ArcGIS. Each 012

tops and sidescan sonar data (Fig. 1). depositional, erosional, and dynamic. Within each class, zebra mussels were absent. polygon has a unique ID and a set of attributes Kilometers sub-classes define the details of the dominant process. contributed by both the sediment type map (Fig. 2) GRAVEL DEPOSITS 41°58'0"N Newburgh, NY 41°58'0"N and the sedimentary environment map (Fig. 3). NEW YORK Danskammer Pt. DYNAMIC AREAS

41°34'0"N 41°34'0"N Wappinger SUMMARY OF KEY RESULTS FUTURE DIRECTIONS Creek 41°28'0"N 41°28'0"N

41°57'0"N 41°57'0"N • Zebra mussels are most often found in areas of coarser grain size, where the • Explore correlations between live zebra mussels and estuary morphology, distance dominant sediment type is sand or gravel. from nearest tributary, mean salinity, and hydrographic parameters. • More than 80% of live zebra mussels in the Kingston-Saugerties area are found • Incorporate zebra mussel sampling data from 6-7 additional areas in the estuary to in dynamic sedimentary environments, particularly areas of debris (potential dump better constrain conditions favorable to zebra mussels.

41°32'0"N • Extrapolate critical parameters to whole estuary to map substrates suitable for 41°32'0"N Storm King 41°56'0"N sites) and scour (moderate to high backscatter, rough surface in bathymetry). Mountain 41°26'0"N 41°56'0"N 41°26'0"N • Live zebra mussels are rarely found in areas where sediment waves are imaged zebra mussel colonization. Beacon, NY New York City (dynamic waves class), although fragments of zebra mussels shells are found. • Consider extent of suitable substrate that falls in saline areas, which may be 74°W 73°58'0"W 74°2'0"W 74°W Rondout 012 Creek • Where live zebra mussels are found in muddy sediments, they are always vulnerable to colonization during wet years or even periods of high river flow Figure 8. Sediment map of north Newburgh Bay, based Figure 9. Sedimentary environment map of south Kilometers ATLANTIC OCEAN classified as regions of dynamic scour in the Kingston-Saugerties area. (e.g. floods, spring freshet). on the combination of grab and core samples and Newburgh Bay, based on all available data. Red circles 41°55'0"N sidescan sonar data. Red circles indicate the presence indicate the presence of live zebra mussels; gray circles 73°58'0"W 73°57'0"W 73°56'0"W 73°55'0"W 73°54'0"W • Although live zebra mussels are often imaged in areas of high sidescan backscatter, of live zebra mussels; gray circles indicate their absence. indicate their absence. Live zebra mussels are found there is no statistical correlation between backscatter value and presence of zebra ACKNOWLEDGEMENTS In this mainly muddy area, live zebra mussels are found near the Newburgh-Beacon bridges, where the estuary Figure 1. Basemap of the Kingston-Saugerties area of the Hudson River Estuary, showing on coarse deposits (gravel lags, tributary deposits). bottom is dominated by dynamic drifts and scour. 100kHz sidescan sonar data. Grab sample sites are shown as circles; red circles indicate mussels in our data for the Kingston-Saugerties area. The Hudson River Benthic Mapping Project is funded by the New York State Dept. of Env. Conservation. live zebra mussels, gray circles indicate no living zebra mussels. Note the presence of live • In the Kingston-Saugerties area, there is no correlation between zebra mussel This research is also supported by the Estuarine Reserves Division, Office of Ocean and Coastal Resource zebra mussels in areas of high sidescan backscatter. presence and water depth or distance to shoreline. Management, National Ocean Service, National Oceanic and Atmospheric Administration. Special thanks go to Dave Strayer from the Institute of Ecosystem Studies in Millbrook, NY for sharing data and insight.