J. Polhemus and Lansbury 1997; J. Polhemus and D. Polhemus 1987, 1990, 1991, 1993, 1994a,b, 1995, 2000, 2001, 2002; Todd 1955, 1959), but with very limited representation of Plecoptera and Megaloptera. In addition, such streams support a rich non-insect macrofauna of fishes (Allen 1991, 1996a, 2003a,b; Allen et al. 2000; Chapter 4.8), crustaceans (Bott 1974; Holthuis 1939, 1950, 1956, 1958, 1982, 1986), and mollusks (Haynes 2001), many of which are diadromous, with marine larval development.
Comprehensive faunal surveys have been undertaken for only a few of the major river basins in Papua, notably the Ajkwa River and portions of immediately adjacent systems (the Minajerwi and Iweka) draining the southern flank of the central ranges in the Timika region (D. Polhemus and J. Polhemus 2000d; Allen et al. 2000); the Wapoga River draining the western section of the central mountain ranges (D. Polhemus 1998; Allen and Renyaan 2000); and the lower reaches of the Idenburg (Taritatu) River (the major eastern branch of the Mamberamo River system) plus various tributaries (the Furu, Doorman, and Tiri) in the vicinity of Dabra (Polhemus 2002; Allen et al. 2002).
DEFINITIONS OF LIMNOLOGICAL TERMS AND UNITS
Physiochemical Measurements
o/oo: parts per thousand, a measure of salinity
% gradient: relative slope measured as the unit of elevational change per 100 horizontal units (as in m/100 m)
µmhos: reciprocal megohms, a measure of water conductivity
Water Regime
Lacustrine (lake-like): deeper open standing waters occupying distinct basins; lakes and ponds
Lentic (standing): water not subject to direct gravitational movement, although internal currents may occur
Limnocrene (spring pool): a pond or pool having a noticeable, discrete, subterranean water source (cf. rheocrene)
Lotic (flowing): water moving unidirectionally in response to substrate altitudinal (elevational) gradient; excludes waters moving in response to wind currents, waves, and tides
Palustrine (marsh-like): shallow standing water visually dominated by emergent vegetation such as mosses, sedges, rushes, trees, etc.
Rheocrene (flowing spring): lotic water from a subterranean source but not in a well-developed channel, and flowing in relatively low and constant volume
Dissolved Minerals
Qualitative aspects
Haline (halinity): brackish or salty water condition wherein dissolved ions are derived from seawater
Saline (salinity): general term for water with noticeable salt content
Quantitative aspects
Limnetic: freshwater, salt content < 0.5 o/oo
Mixohaline: brackish water, salt content 0.5–30 o/oo
Euhaline: seawater, salt content 30–40 o/oo
Hyperhaline: brine-like water, salt content > 40 o/oo
Concentration vs. time
Homiohaline: salt concentration stable or fluctuating only over a narrow range
Poikilohaline: salt concentration fluctuating widely
Ecological Qualifiers
Migration and movement
Amphidromous: type of diadromous animal (see below) that migrates between fresh and marine waters but not for breeding (e.g., sicydiine gobies)
Catadromous: type of diadromous animal that inhabits freshwater but breeds in the ocean (e.g., anguillid eels)
Diadromous: broadly referring to animals (e.g., certain fishes) that obligately migrate between fresh and marine waters during their life cycle
Itinerant: refers to animals that may irregularly or opportunistically migrate between fresh and marine waters (e.g., haline marine fishes sometimes found in streams)
Salt tolerance of biota
Euryhaline/saline: occurs over a wide range of total dissolved solids
Stenohaline/saline: occurs in a narrower range of total dissolved solids
Substrate relationship
Benthic: living on or in the bottom of a water body
Epigeal: living on or above the earth’s surface
Hypogeal: living beneath the earth’s surface (subterranean)
PERENNIAL STREAMS
Perennial streams (Figures 5.5.1–5.5.5) support continuous year-round flow and form the most widely distributed type of lotic ecosystem in Papua. Although the majority are continuous, discharging steadily to the ocean in their natural state, there are certain karst areas, particularly in the central mountain ranges and on the Vogelkop and Bomberai peninsulas, where such streams may be naturally interrupted, with their flow becoming subsurface in their middle or lower sections, although occasionally appearing as scattered pools in areas of bedrock exposure. In larger towns or near industrial developments, streams may also be artificially interrupted via partial or total diversion. Such human-made diversions are generally accompanied by channel alterations that in many instances modify or eliminate the native ecosystem character, particularly in urban areas. Altered streams of this type in lowland areas are often favored habitats for invasive aquatic species.
Because of the relatively intact nature of Papuan forests, the water clarity of undisturbed streams, at least in the smaller order streams of a given network, is generally high except during spates, and dissolved oxygen is normally near saturation throughout most watercourses.
Papuan perennial streams exhibit prominent altitudinal zonation of environmental conditions and biota (Allen et al. 2000; D. Polhemus and J. Polhemus 2000d). This longitudinal continuum may be divided into three broad zones: the headwater, mid-, and terminal reaches, described in greater detail below. Naturally interrupted streams also exhibit a similar zonation, except that the amount of available habitat in their mid- and terminal reaches is often significantly reduced. As such, their diadromous macrofauna, although similar to that of continuous perennial streams, is generally less diverse. Despite this, such streams may contain certain genera of diadromous gobioid fishes that access the upper reaches during intermittent spates that provide temporarily continuous water connections to the sea, and then hold over in the upper reaches until the next flood.
Headwater Reach
Headwater streams (Figure 5.5.1) drain first and second order catchments lying at elevations above 800 m or possessing gradients in excess of 30%; streams of this type in montane regions possess both such attributes. The substratum is usually bedrock or coarse alluvium such as large rocks and boulders; current speeds are generally high; water temperature is less than 18 C (most typically 12–15); conductivity is less than 50 µmhos (with dissolved solids less than 40 mg/l); and pH is often slightly acidic. The fauna of such small, steeply dropping streams is dominated by insects, particularly Ephemeroptera in the family Baetidae, Trichoptera in the families Glossosomatidae, Hydrobiosidae (Apsilochorema), Hydropsychidae (Hydropsyche), Hydroptilidae (Hydroptila), and Leptoceridae (Mystacides, Triae-nodes), Diptera in the families Dolichopodidae and Ephydridae, Odonata in the families
