Methods

I. Study System Lake Mývatn, Iceland (65°36 N, 17°0′ W) is a large (38 km²) 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^-2 yr^-1, averaging 28 g dw m^-2 yr^-1 (Lindegaard and Jónasson 1979). The midge assemblage is mostly comprised of two species (> 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 m²). 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 & 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), “large1” (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 “large2.”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.

Methods

I. Field MethodsThe site where this manipulative field experiment was conducted on the Kalfastrond peninsula at Lake Myvatn is approximately 150 meters long and 75 meters wide. The vegetation consists of grasses Deschampsia spp., Poa spp., and Agrostis spp.), sedges (Carex spp.), and forbs (Ranunculus acris, Geum rivale,and Potentilla palustris). The experimental midge exclusions occurred from the middle or end of May to the beginning of August in each year, the period corresponding to the active growing season of plants and the flight activity of midges at this site. 2 by 2 meter plots were established in 6 blocks spread across the site. Each block included 3 treatment levels, an open control plot, a full exclusion cage and a partial exclusion cage, for a total of 18 experimental plots. Control plots were open to allow complete access to all arthropods. Experimental midge exclusion cages were 1 meter high and constructed from white PVC tubing affixed to rebar posts on each corner of the plot, Plate 1. Full exclusion cages were entirely covered with white polyester netting, 200 holes per square inch, Barre Army Navy Store, Barre VT, USA, to prevent midges from entering the plot. The mesh netting completely enclosed the 2 by 2 by 1 meter frame to prevent flying insects from entering, however the mesh was not secured to the ground in order to allow non flying,ground crawling, arthropods to freely enter and exit the cages. Partial exclusion cages had one 0.5 meter strip of mesh stretched around the outside of the frame and another 0.75 meter strip draped over the top. Partial cages were designed to examine any effects of cages themselves on terrestrial responses while minimally affecting midge inputs into the plots and arthropod movement.The partial exclusion treatment was discontinued in 2011. Each plot contains a pitfall and an infall trap that are continuously sampled during the summer, while the cages are up. Vacuum samples were taken from the plots about once per month in 2008 through 2010 and only once per summer for subsequent summers.Midge activity was measured in all plots to document changes in midge abundance over the course of a season and between years and to assess the degree to which cages excluded midges. Midge abundance in the plots was continuously measured using passive aerial infall traps consisting of a 1000 milliliter clear plastic cup, 95 square centimeter opening, attached to a post 0.5 meters high and filled with 250 milliliters of a 1 to 1 ethylene glycol to water solution and a small amount of unscented detergent to capture and kill insects that alighted upon the surface. Infall traps were emptied about every 10 days.II. AnalysisMidges were counted and identified to morphospecies, small and large. The midge (Diptera,Chrionomidae) assemblage at Myvatn 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), large1 (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 large2.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.

Methods

Riparian samplingPREPARATIONDatasheet packets:Each lake has 8 survey sites.One packet per site:3 10m x 10m riparian zone plot data sheets1 Sapling plot or General Site Info data sheetFor 2 of the 8 sites, packets will need to include 2 riparian subzone data sheets.Weather can be highly variable. Data sheets should be printed on write in rain paper.Survey site selections:8 Sites per lake will be selected using GIS software.Subzones: To look at the effects of wind, sun, and fetch; select 2 of the 8 sites for additional subzone surveys. One site must be located in the NW quarter of the lake and the other in the SE. Within each of these 2 chosen sites, randomly select a 10m x 10m subzone plot in zone 2 and another 10m x 10m subzone plot in zone 3. (See figure 1).Sapling plots: At each site, two 5m x 5m sapling plots should be randomly selected within plots A, C, andoror E (Refer to figure 3).EQUIPMENT LISTClipboard, data sheet packets, lake and site maps, pencils, watch, compass, 50m measuring tapes, Diameter tapes (fabric and combination tapes), flagging, GPS unit,Oars, cushions and vests, motor, gas. Appropriate rain gear and boots.FIELD DATA COLLECTIONRecord the lake name, site number, plot number, date, observers, start and stop time.Collect a GPS point at the start of each of the 8 survey sites (plot A).timesIf the site has to be relocated due to denied permissions, mark new location on lake maps.Prepare Survey Plots:Each site is 30m x 50m in size. Five 10mx10m plots along shoreline are the zone 1 survey plots. Subzones are located in Zones 2 and 3. Plots should never overlap.Set up plots (A, C, E)Facing the selected site location (looking from the water towards shore), plot A is on the left, C and E are to the right of A respectively.Mark the sites starting point (with a flag and a GPS point). Using a meter tape to place flags at 10m increments along the shorelines ordinary high water mark (0m, 10m, 20m, 30m, 40m, 50m).For each 10x10 plot, determine the shoreline aspect, then use a compass and meter tape to place corner flags back 10 meters from shore so that each plot is square.Record the slope and aspect (perpendicular to shore) for the start of plots A, C, and E. This will represent the hills steepness and direction.Recording Data:General site info:Site information must be recorded for all 5 plots (A, B, C, D, and E)Record ownership (public or private).List the number of docks and buildings –count them only once if they cross into 2 plots.Presenceorabsence information – Using the list provided, check anything that is present, or list it as other. Record what is dominant. There are 2 parts to the General site info list:Qualitative assessment of habitat (forest stands, herbaceous, wetlands, etc).Human development andoror disturbance.FOR PLOTS A, C, and E:Live Trees:Record the species and diameter at breast height (DBH) for every living tree that is larger or equal to 5cm DBH (other woody plants having a greater than or equal to 5cm DBH should also be recorded).Diameter at breast height: Since trees are swelled at the base, measurements are made 4.5 feet (1.37 meters) above the ground in order to give an average diameter estimate.Trees on plot edge: Sometimes trees will be questionable as to whether they are in or out of the plot. Good rule of thumb is a 50percent cut off. If the tree is more than 50percent within the plot, count it. Do not count 1 tree in more than one plot!Standing snags: A snag is a (or part of a) dead standing tree taller than 1.37 meters (DBH). If a snag is greater than or equal to 10cm DBH then record type (snag), type of break (natural, un-natural, beaver), species (if known), DBH, and branchiness (0-3).Stumps: A stump is dead tree cut or broken off below 1.37 meters (DBH). Record stumps that are greater than or equal to 10cm in diameter. Take the diameter at the base of the stump but above the root mass. Record type (stump), type of break (natural, un-natural, beaver), species (if known), and diameter at base. Branchiness is assumed to be 0.Coarse Woody Debris (CWD) in Riparian zone:For this study, CWD is considered any logs greater than or equal to 10cm in diameter and greater than or equal to 150cm in length.Record type (log) and type of break (natural, un-natural, beaver, unknown). Record the species type (species, conifer, hardwood, or unknown), the diameter at base, and log length from base to longest branch tip.Record Branchiness (0-3). Where 0 is no branches, 1 is few, 2 is moderate, and 3 is many branches.Record Decay (0-5). Where 0 is a live tree touching the ground at two or more points, 1 is recent downwood (e.g. lacking litter or moss cover), 2 is downwood with litterorhumus or moss cover; bark sound, 3 is bark sloughing from wood; wood still sound, 4 is downwood mostly barkless; staubs loosening; wood beginning to decay; logs becoming oval and in contact with the ground along most of their length, and 5 is decay advanced; pieces of wood blocky and softened; logs becoming elliptically compressed. timestimes NOTE: paper birch retains its bark long after the wood has rotted, score logs of this species by the softness of the wood, not the presenceorabsence of bark. timestimesAdditional parameters:If a log extends out of a plot, record its entire length and measure diameter at the base regardless of whether the base is inside or outside of the plot.If a log crosses into more than one plot, record the entire length and measure diameter at the base, but record log only in the plot where the base is (if the base is outside of the site, then record in the plot closest to the base).Paper birch: often are broken into many small parts. If segments are still in line (no more than ~5 cm separating them), then you can count breaks as a single log.Logs that extend over the water are measured only from the base to the shoreline and listed in notes as measured to water.For each site, Two 5m x 5m sapling plots are randomly selected in plots A, C, andoror E. Use the numbering scheme depicted in graphic.Use compass and meter tape to setup and mark square plots using the original plot aspect.For each sapling plot, count and record all tree saplings greater than 30 centimeters in height but having less than a 5 cm DBH.Subzones:Subzone plot data are recorded the same as plot data.Refer to figure 1 to set up random subplots at 2 of the 8 sites at a lake. Use compass and meter tape to setup and mark square subplots. Use the original plot aspect when possible.For each square 10m x 10m subplot (one in zone 2 and one in zone 3) record slope and aspect.Record all live trees that have greater than or equal to 5cm DBH. Record all stumps greater than or equal to 10cm DBH and snags greater than or equal to 10cm diameter at base. Record logs greater than or equal to 10cm in diameter and greater than or equal to 150cm in length.

Methods

Study Lakes We selected 60 northern temperate lake sites in Vilas County, Wisconsin lake district. Methods for lake choice and sampling are given in greater detail in Marburg et al. (2005) Each lake was sampled once between 2001 and 2004, in June, July, or August (15 different lakes each summer). We chose stratified lakes deeper than 4 m to insure that all the lakes contained a diverse fish community. With two exceptions (chains of lakes), lakes were chosen to be in separate watersheds. Lakes were chosen based on two criteria landscape position, using historical DNR water conductivity data as a proxy of position, and riparian housing development, measured in buildings km-1 shoreline (Marburg et al. 2005). Landscape position refers to the location of a lake along the hydrological gradient. The gradient ranges from the top of a drainage system, where seepage lakes are fed mainly by rainwater, through lakes which receive water from groundwater and have surface outflows, to lakes further down in the drainage system, which receive water from both ground and surface flow (Kratz et al. 1997).Landscape position affects lake water chemistry, because as water flows across the surface and through soil, it picks up carbonates and other ions which increase the waters electrical conductivity (specific conductance, a temperature-independent measure of salinity), alkalinity, and its ability to support algal and macrophyte production. In addition, aspects of lake morphology correlate with landscape position. Most obviously, larger lakes tend to occur lower in drainage systems (Riera et al. 2000).The riparian (near-shore terrestrial) zone around northern Wisconsin lakes is being rapidly developed for use as both summer and permanent housing (Peterson et al., 2003). Concurrent with housing development, humans often directly and indirectly remove logs (Kratz et al. 2002) and aquatic vegetation (Radomski and Goeman 2001) from the littoral zone (near shore shallow water area), resulting in reduced littoral zone complexity. The slowly-decaying logs of fallen trees create physical structure (coarse woody habitat CWH) in the littoral zone of lakes that provides habitat and refuge for aquatic organisms (Christensen et al. 1996). Fish, including plankton-eating species (planktivores), reproduce and develop in shallow water (Becker 1983). Because planktivorous fish affect zooplankton community structure through size-selective predation (Brooks and Dodson 1965), there is the potential for indirect effects of housing development on zooplankton.Lakes ranged in size from 24 to 654 ha. In 2001, 2002 and 2004 we chose lakes from the extreme ends of the conductivity and housing density gradients and in 2003 lakes were chosen to fill in the gap in the middle of the ranges. The study lakes range from oligotrophic to mesotrophic (Kratz et al. 1997 Magnuson et al. 2005).At each lake we sampled zooplankton, water chemistry, riparian and littoral vegetation, fish, crayfish, and macrophytes. Each lake was sampled only once, but given the large number of lakes sampled in this area, we expect to see relationships between variables within lakes and at a landscape scale. A snapshot sampling design maximizes sites that can be visited, and is sufficient for a general characterization of zooplankton communities (Stemberger et al. greater than 001).

Methods

In 2001 - 2004 littoral habitat, fish and macrophyte surveys were performed at eight sites within each of the 55 lakes. The sites were chosen by randomly selecting two points per compass quadrant of each lake. Each year littoral habitat surveys were conducted in June, fish surveys in July and macrophyte surveys in August.Littoral habitat (substrate and coarse woody habitat) was measured along a 50 m transect parallel to shore along the 0.5 meter depth contour at each site. The two Littoral CWH variables (number of logs km-1 greater than 5 cm diameter, and number greater than 10 cm) were transformed by log of (1+number) to normalize the variables.