George W. Kipphut

Arctic lakes and streams as gas conduits to the atmosphere: Implications for tundra carbon budgets

Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric carbon dioxide (CO2) (0.1 to 0.3 petagram of carbon per year) (1 petagram = 1015 grams). But this estimate of carbon balance is only for terrestrial ecosystems. Measurements of the partial pressure of CO2 in 29 aquatic ecosystems across arctic Alaska showed that in most cases (27 of 29) CO2 was released to the atmosphere. This CO2 probably originates in terrestrial environments; erosion of particulate carbon plus ground-water transport of dissolved carbon from tundra contribute to the CO2 flux from surface waters to the atmosphere. If this mechanism is typical of that of other tundra areas, then current estimates of the arctic terrestrial sink for atmospheric CO2 may be 20 percent too high.

The flux of CO2 and CH4 from lakes and rivers in arctic Alaska

Partial pressures of CO2 and CH4 were measured directly or calculated from pH and alkalinity or DIC measurements for 25 lakes and 4 rivers on the North Slope of Alaska. Nearly all waters were super-saturated with respect to atmospheric pressures of CO2 and CH4. Gas fluxes to the atmosphere ranged from −6.5 to 59.8 mmol m−2 d−1 for CO2 and from 0.08 to 1.02 mmol m−2 d−1 for CH4, and were uncorrelated with latitude or lake morphology. Seasonal trends include a buildup of CO2 and CH4 under ice during winter, and often an increased CO2 flux rate in August due to partial lake turnover. Nutrient fertilization experiments resulted in decreased CO2 release from a lake due to photosynthetic uptake, but no change in CO2 release from a river due to the much faster water renewal time. In lakes and rivers the groundwater input of dissolved CO2 and CH4 is supplemented by in-lake respiration of dissolved and particulate carbon washed in from land. The release of carbon from aquatic systems to the atmosphere averaged 24 g C m−2 y−1, and in coastal areas where up to 50% of the surface area is water, this loss equals frac 1/5 to 1/2 of the net carbon accumulation rates estimated for tundra.

Sediment-Water Chemical Exchange in the Coastal Zone Traced by in situ Radon-222 Flux Measurements.

In situ radon-222 flux experiments conducted in benthic chambers in Cape Lookout Bight, a small marine basin on the North Carolina coast, reveal that enhanced chemical transport across the sediment-water interface during summer months is caused by abiogenic bubble tube structures. Transport rates for dissolved radon, methane, and ammonium more than three times greater than those predicted on the basis of molecular diffusion occur when open tubes are maintained by semi-diurnal low-tide bubbling.

Lead-210 sediment geochronology in a changing coastal environment

Abstract Sediment accumulation rate studies utilizing excess 210 Pb and 137 Cs were conducted as part of recent investigations of biogeochemical cycling at a single site in Cape Lookout Bight, a rapidly changing coastal basin on the Outer Banks of North Carolina (U.S.A.). Cores three meters in length reveal a depositional history for the bight interior characterized by a gradual transition in texture from coarse-grained to fine-grained material over the period 1946–1979. This transition is controlled by progressive enclosure of the bight by an active northerly migrating recurved spit. The textural gradation is periodically interrupted by layers of well-sorted sand associated with major storm events. Lead-210 data indicate that the upper meter of the sediment has accumulated at a rate of 3.35 to 4.71 g · cm −2 · yr −1 or approximately 8.4 to 11.8 cm · yr −1 (at o = 0.84). Below 120 cm depth, dilution of clay and silt by low activity sand necessitates correction of the 210 Pb profile in order to establish a geochronology. Grain size 210 Pb distribution measurements at three depths reveal that the specific activity (dpm · g −1 ) of clay is 3.2 times that of silt and 24.7 times that of sand. Corrections of bulk sediment excess 210 Pb activities based on these measurements lead to dates for textural changes which are consistent with charted changes in basin morphology and major storm events. Sixteen 137 Cs measurements between 33–241 cm depth reveal a peak activity at 105–115 cm and indicate a minimum sedimentation rate of approximately 2.7 g · cm −2 · yr −1 .

Biogeochemical cycling in an organic-rich coastal marine basin-3. Dissolved gas transport in methane-saturated sediments

Abstract The transport of dissolved gases in the anoxic sediments of Cape Lookout Bight, North Carolina, is controlled by diffusion and bubble ebullition and exhibits a distinct seasonal cycle. Detailed seasonal profiles of CH 4 , N 2 and 222 Rn and direct gas flux measurements indicate that ebullition dominates the flux of all dissolved gases across the sediment-water interface during summer months, and is of major importance on an annual basis. Transport within the upper 6–8 cm of sediment appears to be controlled by molecular diffusion of gases. Transport at greater depths is controlled by diffusion in winter and ebullition in summer. Rn-222 profiles were used to estimate the rate of stripping of dissolved gases within the CH 4 production zone (10–30 cm); rates averaged 3–5 percent per day and agreed with estimates derived from N 2 profiles. As a result of summer ebullition, the sediments of the bight are never at saturation with respect to the major gases present in seawater. Evidence from other sites suggests that ebullition may be an important transport process in many coastal sediments, and may provide mechanism for the transport of volatile reduced compounds between anoxic sediments and the atmosphere. 222 Rn is a useful tracer for quantifying this transport.

Control mechanisms of arctic lake ecosystems: a limnocorral experiment

To assess the potential impact of human exploitation on arctic lakes and to determine how these eco systems are regulated we initated a limnocorral experiment in Toolik Lake, Alaska, in the summer of 1983. The limnocorrals were 5 m in diameter and from 5–6 m in depth and were open to the sediments. In 1983 four limnocorrals were deployed in an isolated bay of Toolik Lake within a cross-classified treatment regime of high and low inorganic nitrogen and phosphorus additions and high and low free swimming fish additions. The objective of the nutrient addition was to stimulate phytoplankton growth and determine the extent to which increased plant production was passed through pelagic and benthic food chains. The objective of the fish addition was to determine the impact of fish predation on large-bodied zooplankton, especially the zooplanktivorous copepod Heterocope, then to study the effect of altered Heterocope densities on small-bodied zooplankton species population dynamics. In 1984 two more limnocorrals were deployed, one a low fish, 1 × nutrient addition treatment and the other a no fish, no nutrient treatment. The fish manipulation was changed to confining several fish in cages with the cages held in corrals for varying lengths of time.The addition of inorganic nitrogen and phosphorus dramatically increased phytoplankton productivity. This increase in algal biomass and production greatly altered the light environment and water quality in the nutrient treated limnocorrals. The secchi disk depth in the nutrient treated limnocorrals declined each summer reaching as low as 1 m in 1985. Both oxygen content and pH increased in the nutrient treatment corrals. Corrals not receiving nutrient additions remained near lake concentrations for most water quality parameters. While phytoplankton biomass was stimulated in 1983 phytoplankton growth was not sufficient to draw down all the nitrogen and phosphorus added and these nutrients reached high levels in the last half of the summer. In 1984 phosphorus remained above 20 µg in the nutrient-treated corrals but ammonia dropped to reference levels by day 25. In 1985 both nutrient concentrations rapidly declined to reference levels.Most pelagic components responded to the nutrient additions. Microbial production was stimulated in the nutrient treated limnocorrals and bacterial population sizes built up to nearly 8–10 times those of the reference corrals. However, microheterotrophs soon increased in abundance and apparently grazed down bacteria to reference levels. Phytoplankton population density, as estimated by chlorophyll a determinations, increased dramatically with nutrient addition such that each year the phytoplankton densities were higher than before. Primary productivity was also stimulated and appeared not to be light limited even when phytoplankton densities rose to high levels. In the first two years of the experiment zooplankton densities were little altered by the increased phytoplankton densities. However, by 1985 daphnid densities were quite a bit higher in the high nutrient addition limnocorrals.The benthic community and sediment response was much less affected by nutrient addition. Overall sediment respiration increased in the nutrient treated corrals but underlying sediments seemed little affected. Decomposition of Carex litter was likewise little affected by nutrient addition. Benthic invertebrates were also little impacted by the nutrient addition and increased sedimentation of phytoplankton. However, the response of benthic invertebrates is difficult to assess fully in the current experiment because chironomids, a prominent component of the benthic community, failed to recruit into the limnocorrals and the corrals physically shifted during ice-out in the spring of 1984 disturbing the sediment in several corrals.The fish additions in 1983 of free swimming grayling essentially eliminated large bodied zooplankton, especially Heterocope septentrionalis, from all four limnocorrals. In subsequent summers Heterocope were not so dramatically preyed upon but generally were found in higher densities in the low or no fish treatments. However, either when Heterocope were eliminated in 1983 or were in rough inverse proportion to fish density, altered Heterocope abundance had no obvious affect on small-bodied zooplankton abundance. The fish treatment apparently influenced the zooplankton response to high nutrient addition in 1985. In the high nutrient limnocorrals daphnid populations became very abundant, but in the high fish treatment the daphnid responding was the small-bodied D. longiremis while in the low fish treatment the daphnid responding was the large-bodied D. middendorffiana.Thus we have considerable evidence for bottom up control of phytoplankton density and production. This increased production ultimately, but not for two years, stimulated zooplankton density increases. Increased nutrients had little effect on the benthos or sediments. Fish manipulations influenced large-bodied zooplankton but had little effect on small-bodied zooplankton. Because grayling are predominantly plankton feeders in lakes, no fish effect on benthic invertebrates was expected.Limnocorrals thus seem good systems to study nutrient-phytoplankton interactions. They are not as suitable for benthic invertebrate studies and fish manipulations may be difficult. Most other limnocorral studies were of brief duration; however, in the present study the limnocorrals seemed to perform well over a three year period.

The Limnology of Toolik Lake

The scientific study of the Arctic is recent with the exception of various collections and cataloging of plants and animals in the 19th century. The limnological investigation of the Arctic is even more recent with the first review paper of arctic limnology listing only seven papers that dealt with arctic lakes (Rawson, 1953). However, after World War II, research stations developed in arctic Europe, Greenland, and at Point Barrow in Alaska. There was considerable research activity at the Naval Arctic Research Laboratory (NARL) in Barrow (Livingstone et al., 1958; Hobbie, 1964, Chapter 2; Stross and Kangas, 1969), much of which is reviewed by Hobbie (1973).

Biogeochemistry of manganese- and iron-rich sediments in Toolik Lake, Alaska

The sediments within Toolik Lake in arctic Alaska are characterized by extremely low rates of organic matter sedimentation and unusually high concentrations of iron and manganese. Pore water and solid phase measurements of iron, manganese, trace metals, carbon, nitrogen, phosphorus, and sulfur are consistent with the hypothesis that the reduction of organic matter by iron and manganese is the most important biogeochemical reaction within the sediment. Very low rates of dissolved oxygen consumption by the sediments result in an oxidizing environment at the sediment-water interface. This results in high retention of upwardly-diffusing iron and manganese and the formation of metal-enriched sediment. Phosphate in sediment pore waters is strongly adsorbed by the metal-enriched phases. Consequently, fluxes of phosphorus from the sediments to overlying waters are very small and contribute to the oligotrophic nature of the Toolik Lake aquatic system. Toolik Lake contains an unusual type of lacustrine sediment, and in many ways the sediments are similar to those found in oligotrophic oceanic environments.

The Kuparuk River: A Long-Term Study of Biological and Chemical Processes in an Arctic River

Our studies have focused on carbon and nutrient dynamics, primary productivity and decomposition, and abundance and life histories of the macroconsumers in the Kuparuk River in arctic Alaska. The overall objective of these studies is to understand the processes controlling primary and secondary productivity, nutrient dynamics, and trophic structure.

Nutrient Patterns in a Mainstem Reservoir, Kentucky Lake, USA, Over a 10-year Period

ABSTRACT Nutrient patterns were examined spatially and temporally from 1989 to 1998 in Kentucky Lake U.S.A., the largest mainstem reservoir on the Tennessee River system. Nutrients included NO3 −-N, NH4 +-N, PO4 −, SiO2, SO4 −2, and Cl−. Seasonal patterns in most nutrient concentrations were described well by cosine functions. Seasonal descriptions had less variance than discharge related descriptions of nutrient concentrations, possibly due to regulation of reservoir discharge. Differing land-use practices on either side of the reservoir were associated with significantly different nutrient concentrations in their related embayments. The agriculturally dominated western side embayments had lower nutrient concentrations than either the forested eastern side of the reservoir or mainstem sites. Annual average nutrient concentrations did not vary greatly over the 10-year period, indicating no change in eutrophication potential during the sampling period. An exception was a significant decline in SO4 −2 levels from 23 mg·L−1 in 1992 to 12.8 mg·L−1 in 1998. Annual export of nutrients was computed from yearly regressions on seasonal concentrations and daily discharge rates.