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Landscape Interactions Research
Site Location, Descriptions, and Codes
Landscape Interactions Research
Observations (in red);
Experiments (in blue);
Synthesis (in green)
Terrestrial Experimental plots
Moist Acidic Tussock,
Soil water chemistry, C and nutrient production
Water additions to tundra
Moist Acidic Tussock,
Stream flow and chemistry, rain events
Soil water chemistry
Hydrology and biogeochemistry model
Inlet Series of Lakes in the Toolik Basin
Lakes and Streams
Lake and stream chemistry
Lake mixing and primary production
Integration of ecosystems across the landscape
Hydrology and biogeochemistry model
Toolik Lake, Lake
Lakes and their inlet streams
Ecological and chemical impacts of storm events (major
inflows) on lakes
Landscape Site Codes LTER site codes for
of soil water chemistry and catchment export: In 1991 we established a
small experimental watershed (called the "Tussock Watershed") close to
Toolik Lake for further investigation of land-water interactions. The
watershed has an area of about 1.5 ha, is composed mainly of tussock tundra,
and contains a primary stream with a birch and willow riparian zone. There
are three transects of wells and lysimeters in the catchment, and an H-flume
(right, photo by George Kling) is installed to gauge water flow near the
bottom. The study area has been mapped for vegetation, soils, topography,
and landforms at the 1:500 and 1:24,000 scales. The heterogeneity of
landscapes plays a role in the production and export of nutrients and
organic matter. This heterogeneity includes the local effects of water track
or stream gradient and size, and the regional effects of landscape age,
geology and geomorphology, vegetation, and soil composition. For example,
there appears to be a consistent relationship between position on the
drainage slope and groundwater dissolved organic carbon (DOC) concentrations
in the experimental watershed; the relationship is independent of known
effects of vegetation type on DOC, although the processes responsible are
unknown. We maintain standard monitoring of biological and chemical
processes, and are building a GIS database on key parameters such as thaw
depth, soil characteristics, and chemical outputs. The lower part of the
watershed contains an area underlain by glacial material that is only about
15,000 years old, compared to the 100,000 year old material covering the
upper watershed. Because the age of the land surface controls the extent of
weathering, there are large differences between young and old areas in the
amounts of major ions draining into surface waters.
Soil water chemistry is governed by soil moisture, landscape age and
geological substrate, and vegetation. Differences in parent material and
soil age result in landscapes with varying soil pH and vegetation
composition, which result in the "acidic" and "nonacidic" landscapes
common around Toolik and throughout the Arctic.
Recently, we have started extracting soil water from LTER terrestrial
plots over both geologically older (acidic plots) and geologically newer
(nonacidic plots) landscapes (photo right: Kristi Judd and Erica Gwynn
sample soil water at the LTER plots, photo by Alan Streigle). At these
plots we measure the soil water under several treatment areas
(greenhouse (warming), fertilized, and greenhouse+fertilized) and the
control plots. The results of this research will help to determine what
changes occur in soil water chemistry under global climate change
scenarios (warming, increased atmospheric deposition, and increased
precipitation (see Tundra Watering Experiment)). In tundra
ecosystems, soil water is an important component of lake and stream
water due to the shallow thaw depth lack of deep groundwater. Because
soil water is also relatively quickly incorporated into the surface
waters, changes in soil water chemistry can have a large impact on
aquatic systems in addition to terrestrial systems.
Tundra Watering Experiment: To study the effect of
increased precipitation on soil water chemistry and depth of thaw, water has
been added to replicate 5m by 10m plots in the tussock tundra starting in 1996.
Toolik lake water is pumped up the hill into 30 gallon (~120 liter) barrels.
From 1996 to 1998, 30 gallons of lake water were delivered through perforated
tubing to the entire treatment plot, and from 1998 to present, 60 gallons of
lake water are added to the treatment plot each day. There are control plots on
both sides of the treatment plot that receive no additional water. This addition
to the treatment plot approximately doubles the average rainfall during the
sampling season (late June - late August).
Downslope Soil-water Processing: Our initial study site (Shaver et al. 1990; Giblin et al.
1991) was a toposequence of six contrasting ecosystem types in the Sagavanirktok
River valley about 40 km northeast of Toolik Lake. We learned a great deal about
the controls over nutrient cycling as water flowed down the toposequence and
into the river. Each of the six ecosystem types has a major and very different
effect on the total amounts of NO3-, NH4+,
and PO43- in the soil water, which has implications for
the inputs of these nutrients to aquatic systems. Some ecosystem types, like
tussock tundra and dry heath, are major sources of N to soil water. Other
systems, particularly those occurring under or below late-lying snowbanks, are
important N sinks and P sources to soil water. Poorly-drained wet sedge tundra
is a P sink with a remarkably high N mineralization rate.
Impacts on Aquatic Ecosystems: Water entering the
lakes through streams and overland flow carry nutrients and forms of
carbon important to the lake organisms and in the cycling of nutrients. How and
where these materials are delivered to and distributed within the lake is
important to bacteria and primary production. Experiments have been conducted
using dyes to trace water entering Toolik Lake. The inflow cartoon (below, by
Sally MacIntyre) demonstrates the how the cooler water coming from Toolik Inlet
(inflow at far right) mixes thoroughly in the initial shallow basins of Toolik
Lake then flows into the main basins and sinks due to density difference; Above
right, John Hobbie distributes rhodamine, a traceable dye, into E1 inlet into
Toolik Lake using a syringe (photo by George Kling).
Lake Climate Stations: Conditions at
the surface of the lake influence the mixing within the lake and the gas
fluxes at the lake surface. To monitor these conditions, there are two
climate stations, one on Toolik Lake (summers since 1998, and one
station on Lake E5 (summers since 2000. The stations are deployed when
the ice has melted (usually mid-late June - early July) and are removed
in August when the Land-Water team leaves the research station. Both
these stations measure wind speed and direction, air temperature, and
humidity. The Toolik Lake station also measures upwelling and
downwelling, shortwave and longwave radiation (see graph below for
example of net radiation data collected over 6 days in 1999). Photograph
is Toolik Lake Climate Station with Mandy Costa collecting data from
station (photo by Kristi Judd). On the station, the anemometer is
attached to top crossarm (approximately 2.5m above lake surface),
temperature and humidity sensor in the cylindrical radiation shield
approximately half way up main pole (approximately 1.5m above lake
surface), and radiometer on long horizontal arm over water
(approximately 0.5m above lake surface). Note that there are also land
climate stations that are maintained by the Terrestrial group.
Landscape-level controls and scaling: The
inlet stream to Toolik Lake has two major branches (see map below from Kling et
al. 2000). One branch includes a series of eight lakes, I-1 to I-7 and I-swamp.
The other major branch starts in I-8 headwaters and flows only through the
tundra until it reaches lake I-8. It joins the main western branch at I-9, and
together they form the major surface water input to Toolik Lake (see
Impacts on Aquatic Ecosystems).
Both branches have small and similar altitudinal changes (~66m) and similar
lengths. A six year study of the inlet series (Kling et al. 2000) outlined the
spatial and temporal patterns of change and chemical processing within and
between the lakes and streams in this series. In general, processing within the
stream segments (e.g. the inlet to I-Swamp minus the outlet of I-7) has the
opposite trends in production and consumed as within lakes (e.g. the outlet of
I-8 minus the inlet to I-8). For example, potassium and dissolved organic carbon
(DOC) were produced within lakes and consumed within streams. Also, the
magnitude of production in lake sites and consumption in stream sites (or vice
versa) was often similar.
Spatial patterns down the catchment were not apparent in the stream sites. In
the lake sites, there were some patterns of increasing some major ions
(conductivity, some cations, DIC, alkalinity and pH) down the catchment. The
correlation of the given variables between pairs of lakes is called "temporal
coherence" or "synchrony". It was shown that synchrony was negatively related to
proximity of the lakes. Overall synchrony (average of all variables for the lake
pair) was highest between pairs of lakes in close proximity and decreased as the
distance between the lake pair increased. The synchrony of only major ions
showed a similar relationship with the catchment:lake area (rank) ratio.
The inlet series provides an excellent example of the integration of
processing in lakes and in streams at a landscape scale. This study required a
combination of ideas from stream, lake and landscape ecology as well as the
development of a conceptual view of landscape mass balance.
Landscape Carbon Balance: For the most
part the movement of nutrients and other materials is unidirectional from land
to water over geologically short time scales. A notable exception, and perhaps
the most important feedback from water to land involves the cycling of carbon
gases. The cycle begins by fixation of atmospheric CO2 by tundra
vegetation, and the subsequent respiration of plant organic matter in the soil
to produce CO2 and CH4.
shown that these gases then dissolve in groundwater and are transported to lakes
and streams where they are subsequently released to the atmosphere to complete
the cycle. The flux to the atmosphere resulting from excess CO2 and
CH4 in surface waters is a consistent feature of tundra areas. A 1995
study at Toolik lake showed that the magnitude and direction of the CO2
flux is related to the horizontal wind speed with greatest efflux occurring at
medium wind speeds. The feedback of terrestrially produced carbon to the
atmosphere from aquatic systems represents an important flux in the global
carbon cycling of tundra environments, and is related in part to the diversity
of terrestrial vegetation and landscapes. Organic matter in particulate and
dissolved form dominates the nutrient and carbon budgets of arctic surface
waters. While the response of aquatic organisms to dissolved nutrients input
from land is well understood, the response to particulate and dissolved material
washed in from land is less clear. We measure the amounts of these materials
input to Toolik Lake, as well as the effects that these materials have on
bacterial processing of organic matter. Our finding is that some fraction of the
terrestrial DOC washed into the lake greatly stimulates bacterial activity. We
also monitor the chain of lakes along the inlet to Toolik Lake (Landscape-level
controls and scaling) in order to examine the chemical and biological
processing in water as
flows through a series of connected lakes. The results suggest that during
winter and summer the lakes act as reactors which process organic carbon into CO2.
Processing over winter results in a large efflux of CO2 from the
lakes to the atmosphere during spring ice-out, and processing during the summer
results in a smaller but continuous efflux of CO2. On a larger
scale, carbon balance of the entire Kuparuk Basin (9200 km2) was
studied from 1994-1996 and it was found that the aquatic Carbon loss was
40%-100% of terrestrial Net Ecosystem Production.
Summary of Research Results
A program of measurements and process studies has been used to study
the important controls on land-water-atmosphere interactions in the Arctic, and
how these interactions influence ecosystem structure and function. The major
research findings are:
- Experimental manipulation of plant-soil mesocosms showed that hydrologic
flushing and vegetation type are the dominant controls on the production and
export of dissolved carbon from soil waters to lakes and streams.
- Addition of 14CO2 to plant-soil mesocosms showed that
carbon fixed by photosynthesis was rapidly transferred to soil waters as DOC,
dissolved CO2, and dissolved CH4, indicating that recent
photosynthates are important substrates for dissolved carbon production in
- Measurements in soil waters, lakes, and streams indicated a major pathway of
dissolved carbon and trace gas movement from land to surface waters which is
important from small (<0.1 km2) to large (>9000 km2) basin
scales. Enough of this carbon that is lost from land to water is eventually
released to the atmosphere or the ocean to account for ~20-80% of the net
terrestrial carbon exchange with the atmosphere.
- A series of LTER cross-site workshops determined that this land to water to
atmosphere cycling of carbon at landscape-level scales is a common phenomenon
throughout the world, and is not confined to arctic or wetland regions.
- Experiments showed that differences in the quality of the organic carbon
exported from land were related to its place of origin on the landscape and to
the time of season, and this controlled the microbial metabolism of organic
carbon to CO2 in lakes.
- Measurements in a connected series of lakes and streams illustrate that over
small geographic areas, and somewhat independent of lake or stream morphometry,
consistent and directional (downslope) processing of materials helps produce
spatial patterns that are coherent over time for many limnological variables.
These results highlight that the integration of material processing in both
lakes and rivers is critical for understanding the structure and function of
surface waters, especially in a landscape perspective.
- We developed a process model that combines a soil-energy column and water
balance routine with topographic statistics of the watershed. The model predicts
the surface runoff, soil temperatures and respiration, and carbon and nitrogen
residence times for a small watershed near Toolik Lake.
Given our current knowledge of land-water interactions, it is apparent
that three main factors regulate the transformations of terrestrial-derived
materials and their transfers to surface waters: (1) water flow, (2) vegetation
and soil uptake and release, and (3) landscape heterogeneity. Future research
will concentrate on (a) determining the rates of soil production
of dissolved C and nutrients and their transfer to and impacts on surface
waters; (b) quantifying the interactions between different
ecosystems across the landscape; and (c) mechanistic modeling of
the transport of materials from land to water with the goal of predicting the
impacts of future perturbations or global change.
Left: Kama Thieler samples a surface water site on the Inlet Series (photo by
Giblin, A.E., K.J. Nadelhoffer, G.R. Shaver, J.A. Laundre and A.J.
McKerrow. 1991. Biogeochemical diversity along a riverside toposequence in
arctic Alaska. Ecol. Monogr. 61:415-435.
Kling, G.W., G.W. Kipphut, M.M. Miller and W.J. O'Brien (2000) Integration of
lakes and streams in a landscape perspective: the importance of material
processing on spatial patterns and temporal coherence. Freshwater Biology,
Kling, G. W. 1995. Land-water linkages: the influence of terrestrial
diversity on aquatic systems, pp. 297-310. In: F. S. Chapin and C. Korner
(eds.), The Role of Biodiversity in Arctic and Alpine Tundra Ecosystems,
Shaver, G.R., K. J.Nadelhoffer and A. E. Giblin. 1990. Biogeochemical
diversity and element transport in a heterogeneous landscape, the North Slope of
Alaska, pp.105-126. In M.G. Turner and R.H. Gardner (eds.), Quantitative Methods
in Landscape Ecology. Springer-Verlag, New York.
Stieglitz, M., J. Hobbie, A. Giblin, and G. Kling. 1999. Hydrologic modeling
of an arctic watershed: Towards Pan-Arctic predictions. Journal of Geophysical
Research 104, D22, 27507-27518.
Stieglitz, M., A. Giblin, J. Hobbie, M. Williams, and G. Kling. 2000.
Simulating the effects of climate change and climate variability on carbon
dynamics in Arctic tundra. Global Biogeochemical Cycles 14:1123-1136.