US Long-Term Ecological Research Network

Fluxes project at North Temperate Lakes LTER: Predicting Peat Depth in a North Temperate Lake District 2008

Abstract
Peat deposits contain on the order of 1/6 of the Earth's terrestrial fixed carbon (C), but uncertainty in peat depth precludes precise estimates of peat C storage. To assess peat C in the Northern Highlands Lake District (NHLD), a approximately 7000 square km region in northern Wisconsin, United States, with 20 percent peatland by area, we sampled 21 peatlands. In each peatland, peat depth (including basal organic lake sediment, where present) was measured on a grid and interpolated to calculate mean depth. Our study addressed three questions: (1) How spatially variable is peat depth? (2) To what degree can mean peat depth be predicted from other field measurements (water chemistry, water table depth, vegetation cover, slope) and/or remotely sensed spatial data? (3) How much C is stored in NHLD peatlands? Site mean peat depth ranged from 0.1 to 5.1 m. Most of the peatlands had been formed by the in-filling of small lake basins (terrestrialization), and depths up to 15 m were observed. Mean peat depth for small peat basins could be best predicted from basin edge slope at the peatland/upland interface, either measured in the field or calculated from digital elevation (DEM) data (Adj. R2 = 0.70). Upscaling using the DEM-based regression gave a regional mean peat depth of 2.1 plus or minus 0.2 m (including approximately 0.1 to 0.4 m of organic lake sediment) and 144 plus or minus 21 Tg-C in total. As DEM data are widely available, this technique has the potential to improve C storage estimates in regions with peatlands formed primarily by terrestrialization. Number of sites: 21 Sampling Frequency: once for each site
Core Areas
Dataset ID
265
Date Range
-
Maintenance
completed
Metadata Provider
Methods
SamplingAt each location, the extent of the peatland basin was examined visually using the soils map and a long axis was defined as the longest linear stretch of peat, while a short axis was defined perpendicular to the long axis. The sample area of a given site was defined as the entire peatland basin (full basin site, N = 11) if the length of the long axis was 800 m or less. For larger peatlands, the site was defined as an area with width 150-200 m and length 400-600 m (partial basin site, N = 10) extending outward from one edge of the peatland and if possible crossing the entire short axis. Peat depth was measured throughout the area on a regular grid at intervals varying from 20-90 m depending upon the size of the site. In addition, vegetation was surveyed and peat pore water chemistry was sampled at 3 plots located at 25%, 50% and 75% of the length of the long axis of the sampling area. Peat cores were taken at the same plots for a subset of 5 sites described below, and slope at the upland-peatland interface at the edge of the site was also measured for all 11 full basin sites and 4 of the 10 partial basin sites.The depth of organic sediment (primarily peat) was measured to depth of contact with mineral surface (typically sand) throughout the sampling area using a stainless steel peat depth probe (PDP) on a regular grid at intervals varying from 20-90 m. Two different versions of the PDP were used, and intercalibrated to ensure consistency. The first consisted of 60 (1.83 m) sections of 3 800 (0.95 cm) diameter threaded steel rod, connected with hex-shaped coupling nuts. The second was a custom-made version with the same general design including length and diameter of sections, but consisted of a smooth stainless steel surface and contained an inset male and female threading system to avoid the protruding coupling nuts. The PDP was used only to determine depth to refusal and was not equipped to collect samples; thus it could not differentiate between peat and soft organic lacustrine sediment. In nearly all cases, the person using the PDP could feel contact with sand (typical glacial sediments) at depth to refusal.Peat CoresPeat cores were taken at 13 different locations, including the central plot for site 4n and each of the 3 plots for sites 7b, 9b, 12f, and 21b. At each core location, samples were taken using a Russian-style corer (50 cm length, 5cm diameter) at depths of 0.5, 1.0, 2.0, 4.0 and 6.0 m, up to the maximum depth (peat-sand interface). We examined peat color and degree of decomposition using the von Post scale in the field. Particular attention was paid to the presence/absence of gyttja at the peat-sand interface. Gyttja is a dark olive-green algae-derived gelatinous lacustrine sediment, which indicates the former presence of a clear-water lake at a given site.For each core sample (N = 45), a central 10 cm section was preserved and used to measure moisture content, bulk density, and organic matter (OM) content in the laboratory. The 10 cm section was halved vertically, and one half (between 50 and 150 g wet weight) was used for measurement of wet bulk density (rw =mw per V; where mw = wet weight and V = volume measured by water displacement). The other half was used to measure mass loss by oven-drying at 55C until the mass was stable (typically 5-10 days, measurement precision = or - 0.1 g). Volumetric moisture content was calculated as (mw md) per V and bulk density (rb)asmdper V where md =dry weight, mw = wet weight, and V = volume calculated as mw per rw. From the dried sample, a 1-3 g homogenized subsample was ashed in a muffle furnace at 440C for 8 h to determine ash-free dry weight (maf = md mash; precision plus or minus 0.01 g), and OM content (OM%) was calculated as maf per md. Finally, OM density (rOM) was calculated as rb OM%.For each of the 13 core locations, we estimated the total mass of OM by summing the product of rOM and volume over all measurement intervals. To estimate a continuous vertical distribution, rOM was interpolated linearly by depth between measurement points. The 0.25-0.5 m interval was assigned the same rOM as the 0.5 m value, while the 0-0.25 m surface interval was assigned a rOM of half of that measured at 0.5 m, to account for the lower bulk density in living recently dead Sphagnum in the acrotelm. The deepest measured rOM value was extrapolated down to a depth of 0.25 m above the base of the core, and the basal 25 cm of the core was assigned a rOM of 46 kg m3. This is equivalent to the mean value measured for gyttja, to account for the fact that the peat is grading into lower-OM gyttja and or sand at the interface with glacial till. Vertically averaged mean rOM was calculated as the total mass of OM in the core divided by the total core volume.Edge Slope in the FieldBecause many peatlands in this region formed from in-filling of lakes, we hypothesized that local geomorphology, specifically slope at the peatland margin (peatland-upland interface), might be a good indicator of peatland depth. At a subset of 15 sites (including all 11 full basin sites) we measured slope at the peatland-upland interface (Edge Slope in the Field, ESF). At full basin sites, ESF readings were taken at 8 peatland-upland interface locations distributed evenly around the edge of the site. At partial basin sites, measurements were only taken at those site edges that were adjacent to upland, resulting in fewer than 8 locations at each site. At each location, a Suunto clinometer was used to measure slope (%) from the peatland-upland interface oriented up the steepest upland slope at a distance of 5 m, 10 m, 20 m and 30 m, and these four values were averaged to give a single slope value for each location. The precision of individual measurements was plus or minus 0.3% slope (mean SD of replicate measurements). The values used for statistical analysis were site mean (ESFmean) and maximum (ESFmax) of location slopes.VegetationWe hypothesized that the surface vegetation characteristics might be related to peat depth, either directly (due to differential contributions of plant species to decomposition rates and water-holding capacity), or indirectly by responding to local environmental characteristics (e.g., water table, groundwater flow) that also influence peat formation. Vegetation was surveyed following a modification of the U.S. Forest Service Forest Inventory and Analysis (FIA) protocol. At each plot, a circular sampling area with 7.3 m radius was laid out, with 3 linear transects extending from the center to the perimeter at 0, 120 and 240 degrees from compass north. Within the circular plot, all trees with diameter at breast height (DBH) of 2.5 to 4.9 cm were counted as saplings and their species recorded, while species and DBH were recorded for all trees with DBH at 5 cm. Basal area for each tree species in units of m2 ha-1 was calculated by summing the DBH of all individual trees and normalizing by plot area. The mean height and intersection length of each of 4 categories of shrub (alder, bog birch, ericaceous or tree seedling) were recorded for woody vegetation of height greater than 50 cm (but DBH less than 2.5 cm) that intersected any of the linear transects. Shrub percent cover was estimated for each category by dividing the intercepted length by the total transect length. Coarse woody debris (CWD) with length greater than 1 m that intersected any of the linear transects with diameter greater than 5 cm was tallied; small end diameter (down to 5 cm), large end diameter, and length of each piece of CWD was recorded and used to calculate volume as described by Waddell [2002]. Finally, three ground-layer quadrats (1 m2) were laid out, 1 each adjacent to the 3 linear transects spanning a distance of 4 to 5 m from the center point. Within each quadrat, percent cover was recorded for each of 8 commonly occurring ground cover types: bare ground, ericaceous shrubs, ferns, forbs, graminoids, Sphagnum mosses, other mosses, and other woody vegetation (tree seedlings). Values for the 3 quadrats were averaged to give a plot mean cover of each ground cover type.
Short Name
PEAT1
Version Number
24

Little Rock Lake - CWH Study at North Temperate Lakes LTER - Benthic Macroinvertebrates 2002 - 2004

Abstract
Benthic invertebrates were collected as part of CWH (coarse woody habitat) study on Little Rock Lake in Vilas county, WI. Pre-manipulation sampling of the macroinvertebrate communities was conducted in the summer of 2002 before the CWH reduction and six times after the reduction, in early, mid, and late summer (May-August) of 2003 and 2004. We divided the shoreline of Little Rock Lake into 50 m sections and randomly chose five sections from each basin for each separate sampling of macroinvertebrates. We collected two benthos and two CWH macroinvertebrate samples at each section. We constructed a benthos sampler by connecting a SCUBA tank to a 7.6 cm PVC pipe with a hose attached 10 cm from one end of the pipe (Wahle and Steneck 1991; Roth et al. 2007). A 500 m Nitex mesh bag was place at the top end of the pipe furthest from the attached hose. Once the tank was turned on, a vacuum formed that sucked the benthos sample into the bag. We used a 0.09 m2 hoop to delineate the benthos sampling area. We sampled CWH using a self-contained, battery-powered aquatic vacuum with a 500 m Nitex mesh bag (Vander Zanden et al. 2006). Sampling lasted for 30 seconds. All samples were stored in 95% ethanol until processed. Macroinvertebrates were identified to the lowest possible taxonomic level. Helmus M.R. and Sass G.G. (2008) The rapid effects of a whole-lake reduction of coarse woody debris on fish and benthic macroinvertebrates. Freshwater Biology, 53, 1423-1433 Number of sites: 44 Sampling Frequency: once pre-manipulation, 6 sampling regimes after reduction
Core Areas
Dataset ID
230
Date Range
-
LTER Keywords
Maintenance
completed
Metadata Provider
Methods
Benthic invertebrates were collected as part of CWH (coarse woody habitat) study on Little Rock Lake in Vilas county, WI. Pre-manipulation sampling of the macroinvertebrate communities was conducted in the summer of 2002 before the CWH reduction and six times after the reduction, in early, mid, and late summer (May-August) of 2003 and 2004. We divided the shoreline of Little Rock Lake into 50 m sections and randomly chose five sections from each basin for each separate sampling of macroinvertebrates. We collected two benthos and two CWH macroinvertebrate samples at each section. We constructed a benthos sampler by connecting a SCUBA tank to a 7.6 cm PVC pipe with a hose attached 10 cm from one end of the pipe (Wahle and Steneck 1991; Roth et al. 2007). A 500 m Nitex mesh bag was place at the top end of the pipe furthest from the attached hose. Once the tank was turned on, a vacuum formed that sucked the benthos sample into the bag. We used a 0.09 m2 hoop to delineate the benthos sampling area. We sampled CWH using a self-contained, battery-powered aquatic vacuum with a 500 m Nitex mesh bag (Vander Zanden et al. 2006). Sampling lasted for 30 seconds. All samples were stored in 95% ethanol until processed. Macroinvertebrates were identified to the lowest possible taxonomic level. Helmus M.R. and Sass G.G. (2008) The rapid effects of a whole-lake reduction of coarse woody debris on fish and benthic macroinvertebrates. Freshwater Biology, 53, 1423-1433 Number of sites: 44 Sampling Frequency: once pre-manipulation, 6 sampling regimes after reduction
Short Name
HELMUS1
Version Number
25

North Temperate Lakes LTER Northern Highlands Lake District Coarse Woody Debris Trees

Abstract
Coarse woody debris (CWD) is an important, but often neglected, component of lake ecosystems. It is ecologically valuable because it creates littoral habitat complexity but it is susceptible to manipulation by riparian process, in particular removal by property owners. The objective of this study is to determine the spatial scales at which human and environmental factors contribute to coarse woody debris input and output dynamics. Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. CWD was defined as logs: > 2 m length, > 15 cm diameter, mostly submersed in lake, < 25 m from shore, and < 2 m water depth. Locations were determined as average of > 30 dGPS positions. Numbered aluminum tags were attached to each log to facilitate the long-term study of CWD. Return visits to Sparkling and Trout Lakes in 1997 found some tags had been removed by ice or vandals. Heavier tags were attached to these logs. The 1997 re-survey and tag check was not complete.
Dataset ID
139
Date Range
-
Maintenance
completed
Metadata Provider
Methods
Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. Riparian trees with the potential of becoming CWD were measured in Feb. 1997. Locations were determined by differential GPS (greater than 10 points per tree) and diameters were measured as diameter-at-breast-height (dbh) using a "cruising stick" according to the Scribner 78 scale (Philip 1994). Substantial snow cover made nominal "breast height" approximately 200 cm. The entire shores of Crystal and Sparkling Lakes were sampled. Shorelines on the other lakes were selected to represent developed and undeveloped conditions. Approximately 31 percent% (19/61 km) of the total shoreline of the five lakes was surveyed.
Purpose
<p>Tracking locations of trees along shorelines of NTL-LTER primary study lakes.</p>
Short Name
NTLSP006
Version Number
24

North Temperate Lakes LTER Northern Highlands Lake District Coarse Woody Debris Shoreline Development Index

Abstract
Coarse woody debris (CWD) is an important, but often neglected, component of lake ecosystems. It is ecologically valuable because it creates littoral habitat complexity but it is susceptible to manipulation by riparian process, in particular removal by property owners. The objective of this study is to determine the spatial scales at which human and environmental factors contribute to coarse woody debris input and output dynamics. Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. Shorelines were characterized using a qualitative shoreline development index (SDI). The index included: (1) developed and devoid of riparian trees (i.e. lawn, boat launch), (2) few widely spaced trees, (3) some riparian trees and some understory, (4) substantial forest cover, and (5) undeveloped and heavily forested. All 5 lakes were surveyed in June/July 1996. Endpoint positions were determined by greater than 30 dGPS points. Shoreline data were subsequently divided into 10 m segments.
Dataset ID
140
Date Range
-
Maintenance
completed
Metadata Provider
Methods
Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. Shorelines were characterized using a qualitative shoreline development index (SDI). The index included: (1) developed and devoid of riparian trees (i.e. lawn, boat launch), (2) few widely spaced trees, (3) some riparian trees and some understory, (4) substantial forest cover, and (5) undeveloped and heavily forested. All 5 lakes were surveyed in June/July 1996. Endpoint positions were determined by greater than 30 dGPS points. Shoreline data were subsequently divided into 10 m segments.
Purpose
<p>Characterizing shoreline development around NTL-LTER primary study lakes.</p>
Short Name
NTLSP007
Version Number
27

North Temperate Lakes LTER Northern Highlands Lake District Coarse Woody Debris Docks

Abstract
Coarse woody debris (CWD) is an important, but often neglected, component of lake ecosystems. It is ecologically valuable because it creates littoral habitat complexity but it is susceptible to manipulation by riparian process, in particular removal by property owners. The objective of this study is to determine the spatial scales at which human and environmental factors contribute to coarse woody debris input and output dynamics. Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. Boat docks were located on all 5 lakes. Docks were verified in 1997 using digital orthophotos. GPS positions were adjusted to coincide with the photos. Many of the docks were photographed with a digital camera.
Dataset ID
141
Date Range
-
Maintenance
completed
Metadata Provider
Methods
Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. Boat docks were located on all 5 lakes. Docks were verified in 1997 using digital orthophotos. GPS positions were adjusted to coincide with the photos. Many of the docks were photographed with a digital camera.
Purpose
<p>Tracking locations of docks around NTL-LTER primary study lakes.</p>
Short Name
NTLSP008
Version Number
29

North Temperate Lakes LTER Northern Highlands Lake District Coarse Woody Debris Logs

Abstract
Coarse woody debris (CWD) is an important, but often neglected, component of lake ecosystems. It is ecologically valuable because it creates littoral habitat complexity but it is susceptible to manipulation by riparian process, in particular removal by property owners. The objective of this study is to determine the spatial scales at which human and environmental factors contribute to coarse woody debris input and output dynamics. Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (Trout Lake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and Big Muskellunge Lake) were measured in 1996 and 1997. CWD was defined as logs: &gt; 2 m length, &gt; 15 cm diameter, mostly submersed in lake, &lt; 25 m from shore, and &lt; 2 m water depth. Locations were determined as average of &gt; 30 dGPS positions. Numbered aluminum tags were attached to each log to facilitate the long-term study of CWD. Return visits to Sparkling and Trout Lakes in 1997 found some tags had been removed by ice or vandals. Heavier tags were attached to these logs. The 1997 re-survey and tag check was not complete.
Dataset ID
138
Date Range
-
Maintenance
completed
Metadata Provider
Methods
Coarse woody debris, boat docks, and riparian trees (with the potential of becoming CWD) around the five lakes of the NTL-LTER site (TroutLake, Allequash Lake (north basin), Sparkling Lake, Crystal Lake, and BigMuskellunge Lake) were measured in 1996 and 1997. CWD was defined as logs: greater than 2 mlength, greater than 15 cm diameter, mostly submersed in lake, less than 25 m from shore, andless than 2 m water depth. Locations were determined as average of greater than 30 dGPSpositions. Numbered aluminum tags were attached to each log to facilitate thelong-term study of CWD. Return visits to Sparkling and Trout Lakes in 1997 foundsome tags had been removed by ice or vandals. Heavier tags were attached to theselogs. The 1997 re-survey and tag check was not complete.
Purpose
<p>Tracking locations of logs in NTL-LTER primary study lakes.</p>
Short Name
NTLSP005
Version Number
27
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