RESEARCH Effects of Recent Volcanic Eruptions on Aquatic Habitat in the Drift River, Alaska, USA: Implications at Other Cook Inlet Region Volcanoes

RESEARCH Effects of Recent Volcanic Eruptions on Aquatic Habitat in the Drift River, Alaska, USA: Implications at Other Cook Inlet Region Volcanoes JOSEPH M. DORAVA* ciers on the northern and eastern flanks of Redoubt Vol- Alaska Volcano Observatory cano. During and following eruptions in 1989–1990, severe U.S. Geological Survey physical disturbances to the habitat features of the river ad- 4200 University Drive versely affected the fishery. Frequent eruptions at other Cook Anchorage, Alaska 99508, USA Inlet region volcanoes exemplify the potential effects of volcanic activity on Alaska’s important commercial, sport, and ALEXANDER M. MILNER subsistence fisheries. Few studies have documented the Institute of Arctic Biology recovery of aquatic habitat following volcanic eruptions. The University of Alaska Fairbanks eruptions of Redoubt Volcano in 1989–1990 offered an op- Fairbanks, Alaska 99775, USA portunity to examine the recovery of the macroinvertebrate community. Macroinvertebrate community composition and ABSTRACT Numerous drainages supporting productive structure in the Drift River were similar in both undisturbed salmon habitat are surrounded by active volcanoes on the and recently disturbed sites. Additionally, macroinvertebrate west side of Cook Inlet in south-central Alaska. Eruptions samples from sites in nearby undisturbed streams were have caused massive quantities of flowing water and sedi- highly similar to those from some Drift River sites. This simi- ment to enter the river channels emanating from glaciers and larity and the agreement between the Drift River macroinver- snowfields on these volcanoes. Extensive damage to ripar- tebrate community composition and that predicted by a ian and aquatic habitat has commonly resulted, and benthic qualitative model of typical macroinvertebrate communities macroinvertebrate and salmonid communities can be af- in glacier-fed rivers indicate that the Drift River macroinverte- fected. Because of the economic importance of Alaska’s brate community is recovering five years after the distur- fisheries, detrimental effects on salmonid habitat can have bances associated with the most recent eruptions of Re- significant economic implications. The Drift River drains gla- doubt Volcano. Commercial and sport fishery resources of the Cook and that adequate allocations of the remaining fish are Inlet region are economically important to the State of made in a fair way among the various users. This Alaska and generate hundreds of millions of dollars management challenge is undertaken with a series of annually. Additionally, many local residents rely on the tools that includes regulating subsistence, sport, and fisheries for subsistence and recreation. The sockeye, commercial fishing and land uses. However, aligned chinook, coho, pink, and chum salmon fisheries in the along the western side of Cook Inlet are five active Cook Inlet region thrive because much of the surround- volcanoes (Figure 1) that need to be considered in this ing land is undeveloped, water quality is unimpaired, management paradigm. These volcanoes have com- and seasonal streamflows are adequate to support bined to produce more than 90 volcanic eruptions abundant diverse spawning and rearing habitat. Signifi- cant challenges for managers of this fishery are to during the last 10,000 years (Riehle 1985). Recent ensure that adequate riverine habitat is available to eruptions at several of these volcanoes have significantly support the fish, that adequate escapements are allowed affected water quality (Mathisen and Poe 1978, Whet- into the rivers and estuaries to sustain the population, stone 1955, 1956, Wilcox 1959), changed channel geometry (Dorava and others 1993, Waythomas and Dorava 1999), and destroyed riparian vegetation (Dorava KEY WORDS: Aquatic habitat; Volcanoes; Lahars; Lahar-runout flows; and Meyer 1994). These volcanogenic alterations de- Macroinvertebrates; Community structure; Community composition; Taxonomic similarity crease habitat value or degrade it beyond use and many of the physical changes can persist for years (Meyer and *Author to whom correspondence should be addressed. Martinson 1989). Environmental Management Vol. 23, No. 2, pp. 217–230 ௠ 1999 Springer-Verlag New York Inc. 218 J. M. Dorava and A. M. Milner Figure 1. Active volcanoes of the Cook Inlet Region, Alaska. Numerous streams draining volcanoes in the Cook eruption, it is also difficult to assess the effects of an Inlet region provide productive aquatic habitat (Russell eruption on salmon productivity from a specific drain- and National Park Service 1980). Because eruptions in age. Assessing the abundance and distribution of the the Cook Inlet region are relatively frequent—Augus- macroinvertebrate community in these rivers can inte- tine, Spurr, and Redoubt volcanoes have all erupted grate the aquatic habitat conditions over temporal and during the past decade—it is difficult to assess the spatial scales. This assessment also indicates the ability effects of an individual eruption on the regional fishery. of a river to support lower trophic level species and thus Without population information before and after an provide food for upper trophic levels. Volcanic Effects on Alaskan Aquatic Habitat 219 The recovery of biotic communities in rivers follow- stable, resulting in a subsequent predicted increase in ing major volcanogenic disturbances in Alaska has not macroinvertebrate numbers and diversity. Baetidae, previously been examined. In general, the macroinver- Nemouridae, and Chloroperlidae are likely to be the tebrates in Alaska are taxonomically sparse compared first mayfly and stonefly taxa to colonize glacier-fed with those in other North American lowland rivers at rivers, but Diamesinae and Orthocladiinae typically lower latitudes (Oswood and others 1995). The likely remain numerically dominant in the community (Mil- ecological factors that influence this sparseness include ner and Petts 1994). at least the following: ability to withstand freezing, Severe disturbances generated by volcanic eruptions, physiological ability to sustain growth and reproduce in such as complete channel filling, water temperature the face of low cumulative degree-days, and low availabil- increases above the boiling point, and complete denud- ity of carbon to river food webs (Oswood and others ing of riparian areas, lead to recovery through primary 1995). The lower mean annual temperature and lower succession at affected sites. In the Drift River, which has water temperature in higher latitudes also appear to a watershed that is fed by numerous glaciers, one would play a major role in determining the abundance and expect to find a macroinvertebrate community similar distribution of macroinvertebrates in Alaska (Oswood to that in other nearby glacier-fed rivers, except for the and others 1995). severe habitat-altering effects that may be attributed to Based on numerical abundance, macroinvertebrate the most recent eruptions of Redoubt Volcano. This fauna in south-central Alaska are most commonly from study, done in June 1995, examined the macroinverte- the order Ephemeroptera (mayflies), followed closely brate community structure of the Drift River about five by Diptera (trueflies), and in lower numbers by Plecop- years after the last 1989–1990 eruption ended. The tera (stoneflies) and Trichoptera (caddisflies) (Oswood objectives of this study were to: (1) determine the and others 1995). For rivers of glacier origin, the abundance and the community composition and struc- occurrence of macroinvertebrate fauna shifts slightly so ture of macroinvertebrates in the Drift River, (2) evalu- that Diptera are the most common followed by Epheme- ate the recovery of the Drift River by comparing its roptera, Plecoptera, and few or no Trichoptera (Milner macroinvertebrate abundance and its community com- and Petts 1994). position and structure with those in similar nearby The streams draining volcanoes in the Cook Inlet streams not directly affected by the most recent volcanic region are commonly fed by glaciers and their channels activity at Redoubt Volcano, and (3) evaluate salmonid are frequently unstable and shifting, with considerable habitat implication in the Drift River and at other streambed movement. These glacier-fed rivers generally streams draining recently active volcanoes in the Cook provide a migratory pathway for salmon to access Inlet region. clearwater tributaries, where habitat is more suitable. However, glacier-fed rivers can also provide complex Description of the Study Area and valuable habitat for salmonids. Braided reaches provide an abundance of shallow riffle areas, which are Macroinvertebrate samples were collected in 1995 excellent spawning habitat because adequate water from three streams: the Drift River, which drains Re- flows through the streambed gravels providing oxygen doubt Volcano; the Johnson River, which drains Iliamna for incubating salmon eggs. Rearing habitat is provided Volcano; and Cannery Creek, which drains foothills primarily by river margins, in off-channel ponds and near Redoubt Volcano. The Johnson River and Cannery sloughs, or in tributaries where water temperatures are Creek were used as reference sites, representing un- higher and turbidity is lower than those in the main- stressed (by recent volcanic activity) systems with which stem of the river. Milner and Petts (1994) suggest that to compare the Drift River. macroinvertebrate communities in glacier-fed rivers The Drift River originates in the Chigmit Mountains show deterministic

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