Data from: Substantial pulses of aquatic insects emerge from tidal freshwaters along the James River Estuary, Virginia, USA
Data files
Jan 07, 2024 version files 3.70 MB
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emergenceData_daily.csv
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emergenceDataProcessed.csv
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README.md
Abstract
Tidal freshwaters in upper estuarine reaches provide important ecosystem services but are threatened by relative sea-level rise and pollution from increased development. Tidal freshwaters are highly productive and support estuarine and riparian food webs alike. Aquatic insects are common prey subsidies crossing into riparian habitats; however, the magnitude, timing, and composition of insect emergence in tidal systems has received little attention. Our objective was to better understand the magnitude and variability of aquatic insect emergence in tidal freshwaters. To do so, we quantified insect emergence from tidal creeks and estuarine shorelines of the James Estuary, Virginia, USA, and characterized spatial and temporal patterns in the amount of emergent biomass. We continuously monitored insect emergence from 7 April to 8 November 2019 with floating emergence traps to estimate daily emergence, then used generalized additive mixed models to analyze spatial and temporal variation in daily emergence rates. We estimated aquatic insect biomass to emerge at a mean rate (±1 SE) of 15.6 ± 2.0 g dry mass m −2 y −1, which is among the highest of previously published estimates from nontidal systems (mean ±1 SE = 12.9 ± 6.2 g dry mass m −2 y −1 ). Spatial variability in emergence was highly taxon specific. Diptera and Trichoptera had more biomass emerging from the subtidal than intertidal zone, Odonata biomass emerged more from tidal creeks than along the estuarine shoreline, and the amount of Trichoptera biomass increased, whereas Ephemeroptera decreased, with distance from the estuarine shoreline. The magnitude and composition of emergent taxa varied throughout the sampling period, with sequential peaks in biomass that altered the prey available to riparian consumers. Our results suggest that tidal freshwaters export substantial quantities of aquatic insects, which are valuable prey items for riparian consumers in these systems.
README: Data from: Substantial pulses of aquatic insects emerge from tidal freshwaters along the James River Estuary, Virginia, USA
https://doi.org/10.5061/dryad.41ns1rnk1
The dataset emergenceDataProcessed.csv includes standardized biomass and density estimates (m-2 d-1) for each emergent insect taxon collected during the sampling period, as well as covariates used in downstream modeling of insect emergence rates, organized by sample collection (CollectionID).
The dataset emergenceData_daily.csv expands standardized biomass and density estimates (m-2 d-1) to include each emergent insect taxon on each day at each trap during the sampling period, as well as covariates used in downstream modeling of insect emergence rates. Daily estimates can be summed to obtain emergence estimates over longer time periods (e.g., annual estimates, peak emergence estimates). This dataset is created from emergenceDataProcessed.csv and is the input dataset for insect emergence models.
Description of the data and file structure
Each CollectionID (specified as TrapID_CollectionDate) has 7 records, corresponding to the taxa collection during this study.
Taxa is one of 7 taxa identified: Diptera_Nematocera, Ephemeroptera_Pannota, Ephemeroptera_Schistonota, Odonata_Anisoptera, Odonata_Zygoptera, Plecoptera, or Trichoptera.
TrapID includes site and trap number. Each site had 13 emergence traps.
StartDateTime refers to the date and time of trap/sample deployment and is usually the same as the previous collection EndDateTime. Exceptions occur for new trap deployments following instances of missing or damaged traps. StartDateTime == NA if a new trap was deployed for a CollectionID (i.e., trap was not in place during previous collection period).
EndDateTime refers to the date and time of sample collection. Date matches the the CollectionDate in CollectionID. EndDateTime == NA if trap was missing or sample was unusable (e.g., filled with river water, insects not well preserved) for a particular CollectionID.
Duration in days for a sample collection, calculated using EndDateTime - StartDateTime. Duration == NA if either StartDateTime or EndDateTime is missing.
Site of trap location is Deep Bottom Park (DB) or Rice Rivers Center (RC).
Latitude of trap location in decimal degrees.
Longitude of trap location in decimal degrees.
Inundation refers to whether the trap rested on sediment at low tide (Intertidal) or was always over water (Subtidal).
Placement refers to whether the trap was located at the confluence of the creek and estuarine shoreline (Confluence) or at a point along the tidal creek (Creek).
Distance_10m is the distance to the nearest 10m of the trap to the confluence with the estuarine shoreline. Distance was estimated on ArcGIS Pro and was measured along stream length. Traps with Placement == Confluence have Distance_10m == 0.
BiomassSqmDay is the standardized biomass estimate (m-2 d-1) for a collection. If a taxon was not collected in a valid sample (i.e., emergent insects were absent in sample), the the corresponding BiomassSqmDay == 0. If there was not a valid sample for a taxon (i.e., sample compromised, missing data), the corresponding BiomassSqmDay == -1.
CountSqmDay is the standardized density estimate (m-2 d-1) for a collection. If a taxon was not collected in a valid sample (i.e., emergent insects were absent in sample), the the corresponding CountSqmDay == 0. If there was not a valid sample for a taxon (i.e., sample compromised, missing data), the corresponding CountSqmDay == -1.
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Taxa is one of 7 taxa identified: Diptera_Nematocera, Ephemeroptera_Pannota, Ephemeroptera_Schistonota, Odonata_Anisoptera, Odonata_Zygoptera, Plecoptera, or Trichoptera.
TrapID includes site and trap number. Each site had 13 emergence traps.
Site of trap location is Deep Bottom Park (DB) or Rice Rivers Center (RC).
Inundation refers to whether the trap rested on sediment at low tide (Intertidal) or was always over water (Subtidal).
Placement refers to whether the trap was located at the confluence of the creek and estuarine shoreline (Confluence) or at a point along the tidal creek (Creek).
Distance_10m is the distance to the nearest 10m of the trap to the confluence with the estuarine shoreline. Distance was estimated on ArcGIS Pro and was measured along stream length. Traps with Placement == Confluence have Distance_10m == 0.
BiomassSqmDay is the standardized biomass estimate (m-2 d-1) for a specific day. If a taxon was not collected in a valid sample (i.e., emergent insects were absent in sample), the the corresponding BiomassSqmDay == 0. If there was not a valid sample for a taxon (i.e., sample compromised, missing data), the corresponding BiomassSqmDay == NA.
CountSqmDay is the standardized density estimate (m-2 d-1) for a specific day. If a taxon was not collected in a valid sample (i.e., emergent insects were absent in sample), the the corresponding CountSqmDay == 0. If there was not a valid sample for a taxon (i.e., sample compromised, missing data), the corresponding CountSqmDay == NA.
endDate is the date that the estimated emergence occurred (YYYY-MM-DD). Each date within the sampling period (2019-04-07 to 2019-11-08) is included.
Methods
At each site, we placed 4 emergence traps along the estuarine shoreline near the creek–estuary confluence (hereafter, shoreline) and 9 traps longitudinally along the creek, reaching 1050 to 1540 m from the confluence. We positioned all traps within 3 m of the shore (creek or estuarine) at high tide. Variation in water depth resulted in some traps resting on exposed substrate at low tide (intertidal), whereas others always remained over water (subtidal). Additionally, variation in streambank slope resulted in different tidal zone sampling patterns between sites. At Deep Bottom, we sampled Bailey Creek primarily in the subtidal zone and the shoreline primarily in the intertidal zone. At the Rice Center, we sampled Kimages Creek primarily in the intertidal zone and the shoreline primarily in the subtidal zone.
We continuously monitored aquatic insect emergence from 7 April to 8 November 2019, capturing all emergence events within the sampling period. We constructed floating emergence traps following Cadmus et al. (2016) with a few modifications to increase stability and allow for continuous field placement in a tidal system. We used white no-see-um mosquito netting (30.5g/m2 ; Ripstop by the Roll, Durham, North Carolina) to capture small-bodied insects and reduce shading by the trap, which has been found to cause insect avoidance (Davies 1984). We tethered each trap to a 3-m metal conduit pole driven into the sediment to limit drift but allow for vertical movement with tidal changes. Traps covered a basal area of 0.4 m2 and included a collection bottle containing 50 to 100 mL of 70% isopropanol to preserve insects between field collections. We accessed traps by canoe at high tide every 3 to 7 d (mean ±1 SD: 5.1 ± 1.7 d) to collect samples, which is within the range of collection intervals from other studies (e.g., Whiles and Goldowitz 2001, Martin Creuzberg et al. 2017). To collect the most accurate estimate for large-bodied taxa known to avoid emergence traps (MacKenzie and Kaster 2004), we added to the sample large bodied insects (i.e., Odonata, Ephemeroptera) that were found within the trap net but not yet in the collection bottle. We stored samples in 70% isopropanol until processing, which began after the 1 st collection event and continued through August 2020.
We identified the following insects to order or suborder: mayflies (Ephemeroptera, suborders Schistonota and Pannota), stoneflies (Plecoptera), caddisflies (Trichoptera), dragonflies and damselflies (Odonata, suborders Anisoptera and Zygoptera), and aquatic flies (Diptera, suborder Nematocera) based on diagnostic morphological features (Thorp and Covich 2001). We recorded the number of individuals in each order or suborder, dried the insects for 48 h at 60°C in a drying oven, then recorded dry mass (DM) to the nearest 0.1 mg for each sample after equilibration to room temperature. For samples containing many dipterans (>200 ind.; 47% of samples), we counted a representative sample of 100 ind. and pooled the remaining insects. We used the DM of the representative sample and the remaining pooled insects to estimate the total number of dipterans in the sample. We then standardized emergent DM and density estimates from each sample and taxon m–2 d–1 based on trap area and collection interval (mg DM m−2 d−1 and ind. m−2 d−1 ).