US Long-Term Ecological Research Network

LTREB Lake Mývatn Midge Infall 2008-2011

Abstract
Adjacent ecosystems are influenced by organisms that move across boundaries, such as insects with aquatic larval stages and terrestrial adult stages that transport energy and nutrients from water to land. However, the ecosystem-level effect of aquatic insects on land has generally been ignored, perhaps because the organisms themselves are individually small. At the naturally productive Lake Mývatn, Iceland we measured relative midge density on land using passive aerial infall traps during the summers 2008-2011. These traps, a cup with a small amount of lethal preservative, were placed along transects perpendicular to the lake edge and extending ~150-500 m into the shoreline ecosystem and were sampled approximately weekly from May-August. The measurements of midge relative abundance over land were then used to develop a local maximum decay function model to predict proportional midge deposition with distance from the lake (Dreyer et al. <em>in press</em>). In general, peak midge deposition occurrs 20-25 m inland and 70% of midges are deposited within 100 m of shore.
Additional Information
<p>Portions of Abstract and methods edited excerpt from Dreyer et al. <em>in Press</em> which was derived, in part, from these data.</p>
Contact
Dataset ID
306
Date Range
-
Maintenance
On-going
Metadata Provider
Methods
I. Study System Lake Mývatn, Iceland (65&deg;36 N, 17&deg;0&prime; W) is a large (38 km<sup>2</sup>) shallow (4 m max depth) lake divided into two large basins that function mostly as independent hydrologic bodies (Ólafsson 1979). The number of non-biting midge (Diptera: Chironomidae) larvae on the lake bottom is high, but variable: midge production between 1972-74 ranged from 14-100 g ash-free dw m<sup>-2</sup> yr<sup>-1</sup>, averaging 28 g dw m<sup>-2</sup> yr<sup>-1</sup> (Lindegaard and Jónasson 1979). The midge assemblage is mostly comprised of two species (&gt; 90% of total individuals), Chironomus islandicus (Kieffer) and Tanytarsus gracilentus (Holmgren) that feed as larvae in the sediment in silken tubes by scraping diatoms, algae, and detritus off the lake bottom (Lindegaard and Jónasson 1979). At maturity (May-August) midge pupae float to the lake surface, emerge as adults, and fly to land, forming large mating swarms around the lake (Einarsson et al. 2004, Gratton et al. 2008). On land, midges are consumed by terrestrial predators (Dreyer et al. 2012, Gratton et al. 2008), or enter the detrital pool upon death (Gratton et al. 2008, Hoekman et al. 2012). Midge populations naturally cycle with 5-8 year periodicity, with abundances fluctuating by 3-4 orders of magnitude (Einarsson et al. 2002, Ives et al. 2008). II. Midge Infall Measurement We deployed eleven transects of passive, lethal aerial infall traps arrayed at variable distances from Lake Mývatn to estimate relative midge abundance on shore during the summers 2008-2011. Each transect was perpendicular to the lake edge, with traps located at approximately 5, 50, 150, and 500 m (where possible) from shore for a total of 31 traps around the lake. Sampling locations were recorded using GPS and precise distances from the lake were calculated within a geographic information system. Traps consisted of a single 1000 mL clear plastic cup (0.0095 m<sup>2</sup> opening) affixed 1 m above the ground on a stake and filled with 300-500 mL of a 1:1 mixture of water and ethylene glycol and a trace amount of unscented detergent to capture, kill, and preserve insects landing on the surface of the liquid (Gratton et al. 2008, Dreyer et al. 2012). Midges and other insects were emptied from the traps weekly and the traps were reset immediately, thus collections span the entirety of each summer. III. Identification, Counts, and Conversions Midges were counted and identified to morphospecies, small and large. The midge (Diptera,Chrionomidae) assemblage at Mývatn is dominated by two species, Chironomus islandicus (Kieffer)(large, 1.1 mg dw) and Tanytarsus gracilentus (Holmgren)(small, 0.1 mg dw), together comprising 90 percent of total midge abundance (Lindegaard and Jonasson 1979). First, the midges collected in the infall traps were spread out in trays, and counted if there were only a few. Some midges were only identified to the family level of Simuliidae, and other arthropods were counted and categorized as the group, others. Arthropods only identified to the family level Simuliidae or classified as others were not dually counted as Chironomus islandicus or Tanytarsus gracilentus . If there were many midges, generally if there were hundreds to thousands, in an infall trap, subsamples were taken. Subsampling was done using plastic rings that were dropped into the tray. The rings were relatively small compared to the tray, about 2 percent of the area of a tray was represented in a ring. The area inside a ring and the total area of the trays were also measured. Note that different sized rings and trays were used in subsample analysis. These are as follows, trays, small (area of 731 square centimeters), &ldquo;large1&rdquo; (area of 1862.40 square centimeters), and large2 (area of 1247 square centimeters). Rings, standard ring (diameter of 7.30 centimeters, subsample area is 41.85 square centimeters) and small ring (diameter of 6.5 centimeters, subsample area is 33.18 square centimeters). A small ring was only used to subsample trays classified as type &ldquo;large2.&rdquo;The fraction subsampled was then calculated depending on the size of the tray and ring used for the subsample analysis. If the entire tray was counted and no subsampling was done then the fraction subsampled was assigned a value of 1.0. If subsampling was done the fraction subsampled was calculated as the number of subsamples taken multiplied by the fraction of the tray that a subsample ring area covers (number of subsamples multiplied by (ring area divided by tray area)). Note that this is dependent on the tray and ring used for subsample analysis. Finally, the number of midges in an infall trap accounting for subsampling was calculated as the raw count of midges divided by the fraction subsampled (raw count divided by fraction subsampled).Other metrics such as total insects in meters squared per day, and total insect biomass in grams per meter squared day can be calculated with these data. In addition to the estimated average individual midge masses in grams, For 2008 through 2010 average midge masses were calculated as, Tanytarsus equal to .0001104 grams, Chironomus equal to .0010837 grams. For 2011 average midge masses were, Tanytarsus equal to .000182 grams, Chironomus equal to .001268 grams.
Version Number
13

LTREB Lake Mývatn Midge Emergence 2008-2011

Abstract
Adjacent ecosystems are influenced by organisms that move across boundaries, such as insects with aquatic larval stages and terrestrial adult stages that transport energy and nutrients from water to land. However, the ecosystem-level effect of aquatic insects on land has generally been ignored, perhaps because the organisms themselves are individually small. Between 2008-2011 at the naturally productive Lake Myvatn, Iceland we measured total insect emergence from water using emergence traps suspended in the water column. These traps were placed throughout the south basin of Lake Myvatn and were sampled every 1-3 weeks during the summer months (May-August). The goal of this sampling regime was to estimate total midge emergence from Lake Myvatn, with the ultimate goal of predicting, in conjunction with land-based measurements of midge density (see Lake Myvatn Midge Infall 2008-2011) the amount of midges that are deposited on the shoreline of the lake. Estimates from emergence traps between 2008-2011 indicated a range of 0.15 g dw m-2 yr-1 to 3.7 g dw m-2 yr-1, or a whole-lake emergence of 3.1 Mg dw yr-1 to 76 Mg dw yr-1.
Additional Information
<p>Portions of Abstract and methods edited excerpt from Dreyer et al. <em>in Press</em> which was derived, in part, from these data.</p>
Contact
Dataset ID
305
Date Range
-
Maintenance
Ongoing
Metadata Provider
Methods
I. Study System Lake Mývatn, Iceland (65&deg;36 N, 17&deg;0&prime; W) is a large (38 km<sup>2</sup>) shallow (4 m max depth) lake divided into two large basins that function mostly as independent hydrologic bodies (Ólafsson 1979). The number of non-biting midge (Diptera: Chironomidae) larvae on the lake bottom is high, but variable: midge production between 1972-74 ranged from 14-100 g ash-free dw m<sup>-2</sup> yr<sup>-1</sup>, averaging 28 g dw m<sup>-2</sup> yr<sup>-1</sup> (Lindegaard and Jónasson 1979). The midge assemblage is mostly comprised of two species (&gt; 90% of total individuals), Chironomus islandicus (Kieffer) and Tanytarsus gracilentus (Holmgren) that feed as larvae in the sediment in silken tubes by scraping diatoms, algae, and detritus off the lake bottom (Lindegaard and Jónasson 1979). At maturity (May-August) midge pupae float to the lake surface, emerge as adults, and fly to land, forming large mating swarms around the lake (Einarsson et al. 2004, Gratton et al. 2008). On land, midges are consumed by terrestrial predators (Dreyer et al. 2012, Gratton et al. 2008), or enter the detrital pool upon death (Gratton et al. 2008, Hoekman et al. 2012). Midge populations naturally cycle with 5-8 year periodicity, with abundances fluctuating by 3-4 orders of magnitude (Einarsson et al. 2002, Ives et al. 2008). II. Midge Emergence Measurement We used submerged conical traps to estimate midge emergence from Lake Mývatn. Traps were constructed of 2 mm clear polycarbonate plastic (Laird Plastics, Madison, WI) formed into a cone with large-diameter opening of 46 cm (0.17 m<sup>2</sup>). The tops of the cones were open to a diameter of 10 cm, with a clear jar affixed at the apex. The trap was weighted to approximately neutral buoyancy, with the jar at the top containing air to allow mature midges to emerge. Traps were suspended with a nylon line ~1 m below the surface of the lake from an anchored buoy. For sampling, traps were raised to the surface and rapidly inverted, preventing midges from escaping. Jars and traps were thoroughly rinsed with lake water to collect all trapped midges, including unmetamorphosed larvae and pupae, and scrubbed before being returned to the lake to prevent growth of epiphytic algae and colonization by midges. We assume that the emergence traps collect all potentially emerging midges from the sampling area, though it is likely an underestimate, since some midges initially captured could fall out of the trap. Thus, our results should be considered a conservative estimate of potential midge emergence from the surface of the lake.We sampled midge emergence throughout the south basin of Lake Mývatn. Emergence was sampled at six sites in 2008 and 2011 and ten sites in 2009 and 2010, with locations relocated using GPS and natural sightlines. Each site had two traps within 5 m of each other that were monitored during midge activity, approximately from the last week of May to the first week of August. Midge emergence outside of this time frame is extremely low (Lindegaard &amp; Jónasson 1979) and we assume it to be zero. Traps were checked weekly during periods of high emergence (initial and final 2-3 weeks of the study), and bi-weekly during low emergence periods in the middle of the study (July). III. Identification, Counts, and Conversions Midges were counted and identified to morphospecies, small and large. The midge (Diptera,Chrionomidae) assemblage at Mývatn is dominated by two species, Chironomus islandicus (Kieffer)(large, 1.1 mg dw) and Tanytarsus gracilentus (Holmgren)(small, 0.1 mg dw), together comprising 90 percent of total midge abundance (Lindegaard and Jonasson 1979). First, the midges collected in the infall traps were spread out in trays, and counted if there were only a few. Some midges were only identified to the family level of Simuliidae, and other arthropods were counted and categorized as the group, others. Arthropods only identified to the family level Simuliidae or classified as others were not dually counted as Chironomus islandicus or Tanytarsus gracilentus . If there were many midges, generally if there were hundreds to thousands, in an infall trap, subsamples were taken. Subsampling was done using plastic rings that were dropped into the tray. The rings were relatively small compared to the tray, about 2 percent of the area of a tray was represented in a ring. The area inside a ring and the total area of the trays were also measured. Note that different sized rings and trays were used in subsample analysis. These are as follows, trays, small (area of 731 square centimeters), &ldquo;large1&rdquo; (area of 1862.40 square centimeters), and large2 (area of 1247 square centimeters). Rings, standard ring (diameter of 7.30 centimeters, subsample area is 41.85 square centimeters) and small ring (diameter of 6.5 centimeters, subsample area is 33.18 square centimeters). A small ring was only used to subsample trays classified as type &ldquo;large2.&rdquo;The fraction subsampled was then calculated depending on the size of the tray and ring used for the subsample analysis. If the entire tray was counted and no subsampling was done then the fraction subsampled was assigned a value of 1.0. If subsampling was done the fraction subsampled was calculated as the number of subsamples taken multiplied by the fraction of the tray that a subsample ring area covers (number of subsamples multiplied by (ring area divided by tray area)). Note that this is dependent on the tray and ring used for subsample analysis. Finally, the number of midges in an infall trap accounting for subsampling was calculated as the raw count of midges divided by the fraction subsampled (raw count divided by fraction subsampled).Other metrics such as total insects in meters squared per day, and total insect biomass in grams per meter squared day can be calculated with these data. In addition to the estimated average individual midge masses in grams, For 2008 through 2010 average midge masses were calculated as, Tanytarsus equal to .0001104 grams, Chironomus equal to .0010837 grams. For 2011 average midge masses were, Tanytarsus equal to .000182 grams, Chironomus equal to .001268 grams.
Version Number
13

North Temperate Lakes LTER: Phytoplankton - Madison Lakes Area 1995 - current

Abstract
Phytoplankton samples for the 4 southern Wisconsin LTER lakes (Mendota, Monona, Wingra, Fish) have been collected for analysis by LTER since 1995 (1996 Wingra, Fish) when the southern Wisconsin lakes were added to the North Temperate Lakes LTER project. Samples are collected as a composite whole-water sample and are preserved in gluteraldehyde. Composite sample depths are 0-8 meters for Lake Mendota (to conform to samples collected and analyzed since 1990 for a UW/DNR food web research study), and 0-2 meters for the other three lakes. A tube sampler is used for the 0-8 m Lake Mendota samples; samples for the other lakes are obtained by collecting water at 1-meter intervals using a Kemmerer water sampler and compositing the samples in a bucket. Samples are taken in the deep hole region of each lake at the same time and location as other limnological sampling. Phytoplankton samples are analyzed by PhycoTech, Inc., a private lab specializing in phytoplankton analyses (see data protocol for procedures). Samples for Wingra and Fish lakes are archived but not routinely counted. Permanent slide mounts (3 per sample) are prepared for all analyzed Mendota and Monona samples as well as 6 samples per year for Wingra and Fish; the slide mounts are archived at the University of Wisconsin - Madison Zoology Museum. Phytoplankton are identified to species using an inverted microscope (Utermohl technique) and are reported as natural unit (i.e., colonies, filaments, or single cells) densities per mL, cell densities per mL, and algal biovolume densities per mL. Multiple entries for the same species on the same date may be due to different variants or vegetative states - (e.g., colonial or attached vs. free cell.) Biovolumes for individual cells of each species are determined during the counting procedure by obtaining cell measurements needed to calculate volumes for geometric solids (e.g., cylinders, spheres, truncated cones) corresponding to actual cell shapes. Biovolume concentrations are then computed by mulitplying the average cell biovolume by the cell densities in the water sample. Note that one million cubicMicrometers of biovolume PerMilliliter of water are equal to a biovolume concentration of one cubicMillimeterPerMilliliter. Assuming a cell density equal to water, a cubicMillimeterPerMilliliter of biovolume converts to a biomass concentration of one milligramPerLiter. Sampling Frequency: bi-weekly during ice-free season from late March or early April through early September, then every 4 weeks through late November; sampling is conducted usually once during the winter (depending on ice conditions). Number of sites: 4Several taxonomic updates have been made to this dataset February 2013, see methods for details.
Dataset ID
88
Date Range
-
Maintenance
ongoing
Metadata Provider
Methods
Water samples are taken along routine sampling and then prepared into permanent slides by the company Phyco Tech. Slides are available for all years, however, species may not have been determined for all available slides.several taxonomic updates were implemented in February 2013, this includes simple name changes to currently accepted names, changes from genus level to species based on long term experience by Phyco Tech, and some slides were revisited to resolve taxonomic uncertainty.1) Converted all Melosira entries to Aulacoseira. The species names have been changed appropriately. 2) Converted all Oscillatoria entries to Psuedanabaena. The species names have been changed appropriately. 3) Converted all Synedra tenera to Synedra filiformis. 4) Converted all Phacotus entries without a species name to Phacotus
lendneri. 5) Converted all Phormidium mucicola to Psuedanabaena 6) Converted Glenodinium entries without a species name to
Glenodinium quadridens 7) Assume that all other entries with genera names but not species
names cannot be resolved to species. 8) Converted all Chrysococcus entries to Chrysocccus minutus 9) Changed some single-celled Microcystis entries so that they would match the format of the colonial entries (genus + species) 10) Resolved some entries to species that were previously coded incorrectly by genus. 11) Added in Cylindrospermopsis raciborskii entries that were recently recounted and changed from Anabaenopsis raciborskii. 12) Converted all entries of genus Erkenia to Erkenia subaequiciliata
Short Name
NTLPL05
Version Number
29

North Temperate Lakes LTER: Phytoplankton - Trout Lake Area 1984 - current

Abstract
Phytoplankton samples from the seven northern Wisconsin LTER lakes in the Trout Lake area (Allequash, Big Muskellunge, Crystal, Sparkling, and Trout lakes and bog lakes 27-02 [Crystal Bog], and 12-15 [Trout Bog]) are collected six times per year at the deep hole sampling station at the same time as our other limnological sampling is conducted. We use a peristaltic pump and tubing, collecting a separate sample from the epilimnion, metalimnion and hypolimnion for most of the lakes. For 27-2 Bog Lake, which is only 2m deep, we collect one 0-2m composite sample. The samples are preserved with Lugols iodine solution. We create a single hypsometrically pooled composite sample per lake from subsamples of the strata samples. The pooled samples are sent to PhycoTech, Inc., a private lab specializing in phytoplankton analysis, to be made into permanent slide mounts. The slide mounts, 3 slides per sample, are archived at the University of Wisconsin - Madison Zoology Museum Phytoplankton are identified to species using an inverted microscope (Utermohl technique) and are reported as natural unit (i.e., colonies, filaments, or single cells) densities per mL, cell densities per mL, and algal biovolume densities per mL. Multiple entries for the same species on the same date may be due to different variants or vegetative states - (e.g., colonial or attached vs. free cell.) Biovolumes for individual cells of each species are determined during the counting procedure by obtaining cell measurements needed to calculate volumes for geometric solids (e.g., cylinders, spheres, truncated cones) corresponding to actual cell shapes. Biovolume concentrations are then computed by mulitplying the average cell biovolume by the cell densities in the water sample. Note that one million cubicMicrometers of biovolume PerMilliliter of water are equal to a biovolume concentration of one cubicMillimeterPerMilliliter. Assuming a cell density equal to water, a cubicMillimeterPerMilliliter of biovolume converts to a biomass concentration of one milligramPerLiter. Sampling Frequency: 6 samples per year Number of sites: 7
Dataset ID
238
Date Range
-
LTER Keywords
Maintenance
ongoing
Metadata Provider
Methods
Water samples are taken along routine sampling and then prepared into permanent slides by the company Phyco Tech. Slides are available for all years, however, species may not have been determined for all available slides.
Short Name
NTLPL08
Version Number
19
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