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Landscape Interactions Research

 

Our specific Landscape Interaction Research projects are designed to address the general areas shown in our conceptual diagram. These areas are listed below along with the research descriptions. To address how climate, vegetation, and physical setting control the production of materials such as carbon and nutrients in soil waters, we monitor soil water chemistry and catchment export in areas of different geology in the Toolik area. To study how hydrology in turn controls the material export from soils to surface waters, we are conducting a Tundra watering experiment, have studied down slope soil water processing, and have built a hydrological-biogeochemical simulation model (Stieglitz et al. 1999, 2000). These exported materials have Impacts on aquatic ecosystems, and we are studying the impact of storm runoff events on lake ecology. Finally, we are synthesizing our observations in part by determining how these processes scale in space and time as shown in the Landscape Carbon balance and Landscape-level controls and scaling research projects.

 
   

Site Location, Descriptions, and Codes

Landscape Interactions Research Sites

Location

Ecosystem Type

Measurements  Observations (in red); Experiments (in blue); Synthesis (in green)

Terrestrial Experimental plots

Moist Acidic Tussock,
Wet Sedge,
Nonacidic Tussock

Soil water chemistry, C and nutrient production
Water additions to tundra
14
CO2 labeling

Tussock Watershed

Moist Acidic Tussock,
Primary Stream

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 E5

Lakes and their inlet streams

Ecological and chemical impacts of storm events (major inflows) on lakes

Landscape Site Codes LTER site codes for Land-Water sites 

 


 


Monitoring 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 floating 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. We have 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 it 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:

  1. 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.
  2. 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 soils.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.

Future Research:

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 Kristi Judd) 

 

 

 

 


References:

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, 43, 477-497.

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, Springer-Verlag, Berlin.

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.


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