Klamath Lake Research Articles

Structural changes in gills of Lost River suckers exposed to elevated pH and ammonia concentrations

The Lost River sucker ( Deltistes luxatus) is a federally listed, endangered fish that occurs primarily in Upper Klamath Lake—a hypereutrophic lake in southern Oregon, USA. A decline of the sucker population in the lake over the past few decades has been partly attributed to adverse water quality conditions, including elevated pH and ammonia concentrations that occur during summer cyanobacterial blooms. We quantitatively analyzed structural changes in gills of larval Lost River suckers after they were exposed to elevated pH and ammonia concentrations for 30 d. Exposure to pH as high as 10 caused no observed structural changes. However, lamellar thickness and O 2 diffusion distance increased significantly ( P<0.05) at ammonia concentrations that did not significantly decrease survival, growth, whole-body ion concentrations, or swimming performance. Additionally, we qualitatively observed increases in the frequency of hyperplasic and hypertrophic mucous cells, tissue damage, epithelial lifting, and infiltration of white blood cells into paracellular lymphatic spaces at the highest sublethal ammonia concentration. These observed gill changes typically indicate compromised respiratory and ionoregulatory capacity, although such effects were not manifested in the assays we performed . Regardless, these structural gill changes appear to be a more sensitive indicator of exposure to elevated ammonia concentrations than are more traditional sublethal indices. Therefore, gill histopathology might be a relevant early-warning monitoring tool of the health of Lost River suckers in Upper Klamath Lake, and other species in similar eutrophic systems.

Subchronic Toxicity of Low Dissolved Oxygen Concentrations, Elevated pH, and Elevated Ammonia Concentrations to Lost River Suckers

Abstract The Lost River sucker Deltistes luxatus is a federally listed endangered fish species that inhabits hypereutrophic Upper Klamath Lake in southern Oregon. We conducted four subchronic toxicity tests with Lost River suckers by continuously exposing them to low dissolved oxygen (DO) concentrations for 14 d (late juveniles); elevated pH for 30 d (late larvae); elevated ammonia concentrations for 30 d (late larvae); and sublethal ammonia concentrations for 14 d followed by sublethal low DO concentrations for 14 d (early juveniles). Mortality thresholds were approximately 1.4 mg/L in the DO test, more than 10.0 in the pH test (the highest pH tested), and between 0.37 and 0.69 mg NH3-N/L in the ammonia test. Contrary to the common expectation for fish exposed to toxicants, Lost River suckers generally did not display sublethal responses (i.e., reduced growth, altered whole-body ion content, and reduced swimming performance) to low DO concentrations, elevated pH, or elevated ammonia concentrations. In th...

Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements.

The presence of blue-green algae (BGA) toxins in surface waters used for drinking water sources and recreation is receiving increasing attention around the world as a public health concern. However, potential risks from exposure to these toxins in contaminated health food products that contain BGA have been largely ignored. BGA products are commonly consumed in the United States, Canada, and Europe for their putative beneficial effects, including increased energy and elevated mood. Many of these products contain Aphanizomenon flos-aquae, a BGA that is harvested from Upper Klamath Lake (UKL) in southern Oregon, where the growth of a toxic BGA, Microcystis aeruginosa, is a regular occurrence. M. aeruginosa produces compounds called microcystins, which are potent hepatotoxins and probable tumor promoters. Because M. aeruginosa coexists with A. flos-aquae, it can be collected inadvertently during the harvesting process, resulting in microcystin contamination of BGA products. In fall 1996, the Oregon Health Division learned that UKL was experiencing an extensive M. aeruginosa bloom, and an advisory was issued recommending against water contact. The advisory prompted calls from consumers of BGA products, who expressed concern about possible contamination of these products with microcystins. In response, the Oregon Health Division and the Oregon Department of Agriculture established a regulatory limit of 1 microg/g for microcystins in BGA-containing products and tested BGA products for the presence of microcystins. Microcystins were detected in 85 of 87 samples tested, with 63 samples (72%) containing concentrations > 1 microg/g. HPLC and ELISA tentatively identified microcystin-LR, the most toxic microcystin variant, as the predominant congener.

Assessing Potential Health Risks from Microcystin Toxins in Blue-Green Algae Dietary Supplements

The presence of blue-green algae (BGA) toxins in surface waters used for drinking water sources and recreation is receiving increasing attention around the world as a public health concern. However, potential risks from exposure to these toxins in contaminated health food products that contain BGA have been largely ignored. BGA products are commonly consumed in the United States, Canada, and Europe for their putative beneficial effects, including increased energy and elevated mood. Many of these products contain Aphanizomenon flos-aquae, a BGA that is harvested from Upper Klamath Lake (UKL) in southern Oregon, where the growth of a toxic BGA, Microcystis aeruginosa, is a regular occurrence. M. aeruginosa produces compounds called microcystins, which are potent hepatotoxins and probable tumor promoters. Because M. aeruginosa coexists with A. flos-aquae, it can be collected inadvertently during the harvesting process, resulting in microcystin contamination of BGA products. In fall 1996, the Oregon Health Division learned that UKL was experiencing an extensive M. aeruginosa bloom, and an advisory was issued recommending against water contact. The advisory prompted calls from consumers of BGA products, who expressed concern about possible contamination of these products with microcystins. In response, the Oregon Health Division and the Oregon Department of Agriculture established a regulatory limit of 1 microg/g for microcystins in BGA-containing products and tested BGA products for the presence of microcystins. Microcystins were detected in 85 of 87 samples tested, with 63 samples (72%) containing concentrations &gt; 1 microg/g. HPLC and ELISA tentatively identified microcystin-LR, the most toxic microcystin variant, as the predominant congener.

Post-Mazama (7 KA) Faulting Beneath Upper Klamath Lake, Oregon

High-resolution seismic-reflection profiles (3.5 kHz) show that a distinctive, widespread reflection occurs in the sediments beneath Upper Klamath Lake, Oregon. Coring reveals that this reflection is formed by Mazama tephra (MT), about 7 ka in age. The MT horizon is faulted in many places and locally displaced by as much as 3.1 m. Differential displacement of multiple horizons indicates recurrent fault movement, perhaps three episodes since deposition of the Mazama. The pattern of faulting indicates northeast–southwest extension beneath the lake basin.

Harvesting of Aphanizomenon flos-aquae Ralfs ex Born. & Flah. var. flos-aquae (Cyanobacteria) from Klamath Lake for human dietary use

In western cultures, certain cyanobacteria have beenan accepted source of microalgal biomass for food forabout 30 years, in particular Spirulina(Arthrospira) platensis and S. maxima. Beginning in the early 1980s, another species, Aphanizomenon flos-aquae was adopted for similaruses. This is harvested from Upper Klamath Lake, thelargest freshwater lake system in Oregon. In 1998 theannual commercial production of Aphanizomenonflos-aquae was about 1 × 106 kg. Since thisspecies is not cultured like Spirulina inoutdoor ponds or raceways, it requires very differentprocedures for harvesting and processing. These arereviewed here and include extensive off-lake screensor on-lake barges, which dewater and concentrate thecells. Other procedures, such as those for removal ofdetritus and mineral materials, and those formonitoring and reducing the amounts of certaincontaminant cyanobacteria, which can producecyanotoxins, have also become important in qualitycontrol and marketing.

Estimating the probability of exceeding elevated pH values critical to fish populations in a hypereutrophic lake

Current eutrophication models typically are used to predict seasonal mean conditions. However, the risk of summer fish kills in hypereutrophic lakes is likely to be more closely dependent on periodic extreme events, such as potentially lethal peaks in pH driven by algal photosynthesis. In hypereutrophic Upper Klamath and Agency lakes, Oregon, peak summertime pH values frequently exceed critical levels that can reduce fish growth and survival (pH &gt; 9.50, a likely sublethal tolerance limit for two resident endangered fish species). We developed two empirical models, one parametric and one nonparametric, that predict the likelihood of exceeding user-defined critical values of pH from concentrations of chlorophyll a in these lakes. Separate models were derived to incorporate seasonal dynamics and differences between the two lakes, and the behavior of these models was tested under four different critical pH scenarios. Both parametric and nonparametric models performed similarly, suggesting that management efforts to reduce chlorophyll a in these lakes from 200 to 100 µg·L-1 should decrease the probability of exceeding pH 9.5 by 45%. We suggest that this general approach potentially can be applied to the management of fish populations in other hypereutrophic lakes as well.

Risk Assessment of Microcystin in Dietary Aphanizomenon flos-aquae

Aphanizomenon flos-aquae, a cyanobacterium that is marketed as a health food supplement, is harvested from natural blooms in Klamath Lake (Oregon) that are occasionally contaminated by Microcystis spp. Regulatory agencies in several countries are developing regulations to control the amount of microcystin in drinking water and other products, including products produced from A. flos-aquae. Regulation of microcystin (MC), a toxin produced by Microcystis spp. that is potentially present in natural culture of A. flos-aquae, should be based on studies in which a test species is exposed to the natural mixture of these cyanobacteria. A 1984 feeding trial to determine the effects of high dietary levels of A. flos-aquae on reproduction and development of mice is reanalyzed in light of recent analyses for microcystin-LR (MCLR) in the diets of those mice. Young adult mice consuming up to 333 μg MCLR/kg body weight (bw)/day exhibited no adverse effects on growth and reproduction, fetal development, and survival and organ weights of neonates. Based on a NOAEL of 333 μg MCLR/kg bw/day, a safety factor of 1000, consumption of 2 g/day of A. flos-aquae by a 60-kg adult, the safe level of MCLR as a contaminant of A. flos-aquae products is calculated to be 10.0 μg MCLR/g.

Effects of Ambient Water Quality on the Endangered Lost River Sucker in Upper Klamath Lake, Oregon

Abstract Populations of the Lost River sucker Deltistes luxatus have declined so precipitously in the Upper Klamath Basin of Oregon and California that this fish was recently listed for federal protection as an endangered species. Although Upper Klamath Lake is a major refuge for this species, fish in the lake occasionally experience mass mortalities during summer and early fall. This field study was implemented to determine if fish mortalities resulted from degraded water quality conditions associated with seasonal blooms of phytoplankton, especially Aphanizomenon flos-aquae. Our results indicated that fish mortality did not always increase as water temperature, pH, and un-ionized ammonia concentration increased in Upper Klamath Lake. Little or no mortality occurred when these water quality variables attained their maximum values. On the other hand, an inverse relation existed between fish mortality and dissolved oxygen concentration. High mortality (>90%) occurred whenever dissolved oxygen concentration...

Lethal levels of selected water quality variables to larval and juvenile Lost River and shortnose suckers

Resource managers hypothesize that occasional fish kills during summer–early fall in Upper Klamath Lake, Oregon, may be linked to unfavorable water quality conditions created by massive algal blooms. In a preliminary effort to address this concern, short-term (96-h-long) laboratory tests were conducted with larval and juvenile Lost River ( Deltistes luxatus) and shortnose ( Chasmistes brevirostris) suckers to determine the upper median lethal concentrations (LC 50s; also referred to as median tolerance limits) for pH, un-ionized ammonia, and water temperature, and the lower LC 50s for dissolved oxygen. The mean LC 50s varied among species and life stages as follows: for pH, 10.30–10.39; for un-ionized ammonia, 0.48–1.06 mg litre −1; for temperature, 30.35–31.82°C; and for dissolved oxygen, 1.34–2.10 mg litre −1. Comparisons of 95% confidence limits indicated that, on average, the 96-h LC 50s were not significantly different from those computed for shorter exposure times (i.e., 24 h, 48 h, and 72 h). According to two-way analysis of variance, LC 50s for the four water quality variables did not vary significantly ( p>0.05) between fish species. However, LC 50s for pH (exposure times of 24 h and 48 h) and dissolved oxygen (exposure times of 48 h, 72 h, and 96 h) differed significantly ( p≤0.05) between life stages, whereas LC 50s for un-ionized ammonia and water temperature did not exhibit significant differences. In general, larvae were more sensitive than juveniles to high pH and low dissolved oxygen concentrations. When compared to ambient water quality conditions in Upper Klamath Lake, our results strongly suggest that near-anoxic conditions associated with the senescence phase of algal blooms are most likely to cause high mortalities of larval and juvenile suckers.

Late Quaternary slip rate and seismic hazards of the West Klamath Lake fault zone near Crater Lake, Oregon Cascades

Crater Lake caldera is at the north end of the Klamath graben, where this N10°W-trending major Basin and Range structure impinges upon the north-south–trending High Cascades volcanic arc. East-facing normal faults, typically 10–15 km long, form the West Klamath Lake fault zone, which bounds the graben on its west side. The fault zone terminates on the south near the epicentral area of the September 1993 Klamath Falls earthquakes. It continues north past Crater Lake as the Annie Spring fault, which is within ∼1 km of the west caldera rim, and Red Cone Spring fault. We have determined a long-term vertical slip rate of 0.3 mm/yr for these two faults using high-precision K-Ar and 40 Ar/ 39 Ar age measurements on offset lava flows ranging in age from ca. 35 to 300 ka. Holocene offset reported by Hawkins et al. and epicenters of eight M W 2 earthquakes in 1994 and 1995 indicate that the West Klamath Lake fault zone is active. Empirical relations between earthquake magnitudes and scarp heights or fault lengths suggest that the fault zone is capable of producing earthquakes as large as M W 7¼. Earthquakes on these or other faults of the zone could trigger landslides and rockfalls from the walls of the caldera, possibly resulting in large waves on Crater Lake.

Agriculture and endangered species: An analysis of trade‐offs in the Klamath Basin, Oregon

In 1988 the U.S. Fish and Wildlife Service, under provisions of the Endangered Species Act (ESA), declared two fish species in the Klamath Basin as endangered and mandated minimum water levels in Upper Klamath Lake to protect habitat for these species. The lake is the key hydrological feature of the basin; inflows and lake storage provide irrigation water for over 220,000 acres (890.34 km2) in the area. The ESA lake level restrictions reduced both expected average irrigation water supplies and the capacity of the lake to stabilize water supplies during drought cycles. This research explores trade‐offs between lake levels for fish protection and the profits of farmers under a range of lake level and farmer adaptations. The results indicate that farmers can adjust their irrigation decisions to offset some of the water supply reductions. However, there are costs to agriculture. The expected average cost of maintaining ESA lake levels (estimated over 73 water years) is approximately $2 million annually; for severe drought years, annual costs exceed $15 million or about 60% of average farm profits. The steeply increasing marginal cost curve shows an increasingly heavier economic burden to agriculture as lake level restrictions increase.

The 1993 Klamath Falls, Oregon, earthquake sequence: Source mechanisms from regional data

We use regional broadband seismograms to obtain seismic moment‐tensor solutions of the two September 20, 1993, Mw=6, Klamath Falls, Oregon earthquakes, their foreshock and largest aftershocks (MD&gt;3.5). Several sub‐groups with internally consistent solutions indicate activity on several fault segments and faults. From the estimated moment‐tensors and depths of the main shocks and from the aftershock distribution we deduce that both main shocks occurred on an east‐dipping normal fault, possibly related to the Lake of the Woods fault system. Rotation of T‐axes between the two main shocks is consistent with the two dominant trends of the aftershocks and mapped faults. We propose that a change in fault strike acted as temporary barrier separating the rupture of the main shocks. Empirical Green's function analysis shows that the first main event had a longer rupture duration (half‐duration 1.7 s) than the second (1.2 s). In December, vigorous shallow activity commenced near Klamath Lake's western shore, 5–10 km east of the primary aftershock zone. It appears a Mw=5.5 aftershock occurring the day before, though within the primary aftershock zone, triggered the activity.

A taxonomic reappraisal of someStephanodiscusspecies (Bacillariophyta)

The following species are examined: Cyclotella minutula Kutzing, Stephanodiscus minutus H. L. Smith Type 504, Grunow in Cleve & Moller 221, S. oregoniae H. L. Smith Type 506, Discoplea oregonica Ehrenberg, Stephanodiscus carconensis Grunow var. carconensis, S. carconensis var. minor Grunow, and S. carconensis var. pusillus Grunow. The study is based on original material, drawings, and annotations from collections or exsiccata of Kutzing, Ehrenberg, H. L. Smith, Cleve & Moller, and Moller, and where possible also on light and electron microscope studies of unmounted type material. The results show both morphological differences and similarities between the observed species. The material on slides 504 (H. L. Smith) and 221 (Cleve et Moller) are identical. The material on slide 506 (H. L. Smith, Klamath Lake) is identical with that from the Grunow collection (slide 2007, Klamath Lake). The name Stephanodiscus minutus has never been validly published, and has been widely misused, but the diatom to which it wa...

A Test of Water Depth Niche Partitioning by Western Grebe Color Morphs

Darkand light-phase Western Grebes (Aechmophorus occidentalis) have been described by Storer (1965) and Ratti (1981). Ratti (1979) and Nuechterlein (1981) reported on reproductive separation and isolating mechanisms between color morphs. Data from Ratti (1979) indicate that light-phase birds represent reproductively independent populations and that morphs are separate species. Ratti (1979) stated that morphologically and ecologically, darkand light-phase Western Grebes are practically indistinguishable and may represent one of best avian examples of an exception to competitive exclusion principle (Grinnell 1904). However, Nuechterlein (1981) reported that light-phase birds tend to feed farther from shore than dark-phase birds. He also noted a preponderance of level dives by dark-phase birds and a preponderance of springing dives by light-phase birds. The light-phase diving posture is more perpendicular to water surface and may facilitate diving to greater These findings led to Nuechterlein's (1981) hypothesis that the two color phases may be segregating behaviorally into two subtly different ecological forms specialized for feeding at different depths. The objective of this research was to test Nuechterlein's (1981) hypotheses. Data were gathered at Goose Lake, Lower Klamath National Wildlife Refuge (NWR), and Tule Lake NWR, California; Upper Klamath Lake, Oregon; and Bear River NWR, Utah. Goose and Upper Klamath lakes are natural water basins; Lower Klamath, Tule Lake, and Bear River NWRs are artificial water impoundments. All surveys were initiated at sunrise, when most birds were actively feeding, and usually terminated by midmorning. Survey routes were determined from previous field work (Ratti 1979). One survey was conducted at each study area and, thus, all data are statistically independent. Birds were classified as dark-phase or light-phase (Ratti 1981); rare intermediates were not recorded. Each bird observed was recorded into 1 of 3 categories, based on an ocular estimation of distance from shore; A = 75 m. The location, number of birds, and color phase also were recorded on a map of survey route. After completion of bird surveys, I returned to bird observation sites and conducted a minimum of 3 water-depth transects. Transect lines were 100 m apart, parallel, and generally perpendicular to shoreline of observation site. I traversed transect lines from a canoe, and recorded water depth from ocular estimated distances of 15, 50, and 100 m from shore to correspond with distance categories of bird observations. Throughout study, distances were measured periodically from shore to verify my ocular estimations. Data from bird observations were tested using Chi-square analysis and mean depths were compared by t-test. Between 15 June and 20 July 1981, I observed 1,132 dark-phase and 596 light-phase Western Grebes and measured water depth from 106 transects. Variation in number of water-depth transects measured at each location was a function of distribution of birds along survey route. Distance from shore.-Observations of color morphs in categories of distance from shore were not random (Table 1). There was a clear tendency for

Organochlorine chemical residues in white pelicans and western grebes from the klamath basin, california

Samples were analyzed for 12 organochlorine chemicals. Concentrations of DDT + DDD and dieldrin in American white pelican(Pelecanus erythrorhynchos) eggs collected at the Klamath Basin National Wildlife Refuges decreased from 1969 to 1981; DDE and polychlorobiphenyl (PCB) residues did not significantly change. Differences between PCB residues in eggs collected from Lower Klamath and Clear Lake colonies in 1969 suggest different migration routes or wintering areas between populations nesting at these two locations. White pelican and western grebe(Aechmophorus occidentalis) PCB/DDE ratios were 0.13 and 1.58, respectively, suggesting different exposure patterns. White pelican eggshell thickness increased between 1969 and 1981, but remained significantly less than pre-1947 values. Western grebe shell thickness was not significantly different from pre-1947 values. Endrin caused some of the pelican mortalities in the Klamath Basin from 1975 to 1981. Pelicans may have acquired endrin in California, but possibly from areas outside of the Klamath Basin.

Effects of Nitrogen Fertilization on Manganese Concentration and Yield of Barley and Oats

AbstractResponse of barley (Hordeum vulgare L.) and oats (Avena sativa L.) to band application of N sources with and without Mn and the effects of band vs. broadcast application of fertilizers on the Mn concentration in leaves and yield of barley and oats were studied in the field in 1978, 1979, and 1980 on Lower Klamath Lake where Mn deficiency of oats had been observed in previous years. Experiments were established on a Tulana silt loam variant (medial, nonacid, mesic, Mollic, Andequepts). The pH of the soils ranged from 7.6 to 8.3 and the organic matter content was between 17 and 19%. Nitrogen was applied at 0, 22, or 45 kg N/ha as (NH4)2SO4, NH4Cl, urea, and various urea‐phosphate (UP) formulations. Manganese was applied at 0 or 5.6 kg Mn/ha as MnSO4. All treatments received P at 19 kg P/ha as Ca(H2PO4)2 or 25 kg P/ha in the UP fertilizers, and Cu as CuSO4 at 2.2 kg Cu/ha in 1978 and 5.6 kg Cu/ha in 1979 and 1980. ‘Cayuse’ oats and ‘Steptoe’ barley were planted at 110 kg/ha. Band application with the seed of 22 or 45 kg N/ha as (NH4)2SO4 or NH4Cl significantly increased both barley and oat leaf Mn concentrations and yields all 3 yr. Leaf Mn concentrations and yields were not increased by urea fertilization. When Mn was applied with the N fertilizer, leaf Mn concentrations and yields were similar regardless of N source. Broadcast application of fertilizers did not increase leaf Mn concentration or yield. The UP materials were intermediate in effectiveness between urea and (NH4)2SO4.

Distribution and Productivity of Nesting Bald Eagles in Oregon, 1978-1982

Although little has been published on breeding Bald Eagles (Haliaeetus leucocephalus) in Oregon, various authors have commented on their distribution and abundance. Woodcock (1902) listed the Bald Eagle as common along the Columbia River, at Klamath Lake, and near Haines in Baker County; not common around Beaverton in Washington County and Elkton in Douglas County; and rare in Tillamook County and near Scio in Linn County. Gabrielson and Jewett (1940) listed the Bald Eagle as an uncommon resident along larger waterways and the high Cascade lakes and more common along the coast. Elzroth and Ramsey (1979) categorized the species as an uncommon, permanent resident along the coast, on lakes, and along rivers throughout the state. The present paper summarizes five years of observation of breeding Bald Eagles in Oregon. Objectives of the study were to determine the number and distribution of breeding pairs, describe breeding chronology, and determine activity and productivity at nest sites.

Facieplatycauda pratti gen. n., sp. n. and Two New Species of Myxobolus (Myxosporida)*

Synopsis.Facieplatycauda pratti gen. n., sp. n. and Myxobolus kozloffi sp. n., from the Klamath Lake sucker,Catostomus luxatus (Cope), are described. The new genus is placed in the family Myxobolidae between Henneguya and Myxobolus. The spore valves beyond the sporoplasmic space are broad and long but not attenuated as an inverted triangle as in certain species of Myxobolus with tails, or of Henneguya with sometimes bifurcated tails. An organism resembling Myxobolus insidiosus (Wyatt &amp; Pratt) was found in the muscle of the body of Salmo clarki (Richardson). Differences in spore structure and site of infection suggest this is a subspecies of the previous form which should be designated Myxobolus insidiosus clarki. A previously unreported species of Myxobolus from Cottus aleuticus (Gilbert) is also described.

Heat flow data and their relation to observed geothermal phenomena near Klamath Falls, Oregon

Two holes were drilled to depths of about 180 m in the Lower Klamath Lake basin south of Klamath Falls, Oregon, to obtain heat flow data and to provide estimates of the thermal conductivity of the valley fill. Twenty-nine thermal conductivity determinations on eight cores give a mean conductivity of 1.82 mcal/cm s °C (0.75 W/m °K). Curvature in the upper 50 m of both terriperature profiles indicates a decrease in surface temperature of about 1.8°C, presumably resulting frorn reclamation of what was marshland in the early part of this century. A surprisingly low heat flow of 0.3 HFU (1 HFU = 10−6 cal/cm2 s = 41.8 mW/m2) was measured at site LS near the center of the basin. At site OC-1, 7 km east of LS and 2 km from the Klamath Hills geothermal zone, the heat flow was 1.44 HFU, also a low value in this setting. Temperature profiles in 15 unused water wells in the area had linear gradients ranging from 47° to 170°C/km. The corresponding lower limits of heat flow (conductivities measured at the two heat flow sites being used) range from 0.8 to 3.1 HFU. These variations in heat flow evidently are caused by temperature variations in a convecting system within the near-surface volcanic rocks and do not provide firm constraints on the nature of heat sources at depth.