Hydrometridae (Hydrometra), Veliidae (Microvelia), Notonectidae (Enithares, Anisops), Corixidae (Micronecta), and various aquatic Coleoptera in the families Dytiscidae, Hydrophilidae, and Gyrinidae (Macrogyrus).
Figure 5.5.5. The Tirawiwa River upstream from its confluence with the Wapoga River, in north-central New Guinea, is typical of a low gradient, terminal reach river flowing across alluvial lowland terrane.
Photo: D. A. Polhemus.
Figure 5.5.6. Overflow channels, such as this one along a tributary to the Doorman River near Dabra, in north-central Papua, function as intermittent streams, carrying surface flow during the wet season and then receding to scattered pools fed by hyporheic flow during the drier months of the year.
Photo: D. A. Polhemus.
RHEOCRENES
Rheocrenes, literally ‘‘flowing springs,’’ are perennial seeps and springs flowing short distances over rock surfaces (Figure 5.5.7) or in indistinct channels. These numerous, ubiquitous small seepages (which represent ‘‘leaks’’ from elevated aquifers) are typically found as natural occurrences on bedrock faces or banks of deeply incised streams (particularly adjacent to waterfalls), as well as artificially along road cuts. Water quality of such ecosystems is variable, with their waters sometimes iron-rich as evidenced by bacterial precipitation of orange ferric hydroxide. Two divisions can be recognized: thermal, with average water temperature noticeably (at least 10 C) above the mean annual temperature of the air at the same locality, and non-thermal, with water temperature near or below the mean annual air temperature.
Figure 5.5.7. Rheocrenes, such as this seeping bedrock face and outflow pool near Etna Bay, are common in the mountains of New Guinea and support a highly specialized insect biota rich in endemic Coleoptera, Heteroptera, and Odonata.
Photo: D. A. Polhemus.
Non-thermal rheocrenes, by far the most common type, have a distinctive and often highly endemic biota consisting of a flora of algae, mosses, ferns, Diptera in the family Dolichopodidae, Odonata in the families Megapodagrionidae (Argiolestes) and Corduliidae (Hemicordulia), Coleoptera in the families Dytiscidae and Hydrophilidae, and Heteroptera in the families Gelastocoridae (Nerthra), Ochteridae (Ochterus), Hebridae (Hebrus), Saldidae (Saldula), and Microveliinae (Aegilipsicola, Rheovelia, Brechyvelia). Although they may support distinct algal communities, thermal rheocrenes in general tend to have a highly impoverished fauna, as is typical of thermal waters in general throughout Papua.
ARTIFICIAL DITCHES AND FLUMES
Ditches and flumes are artificial streams constructed by humans to convey water to areas where it would otherwise not naturally flow. Such conduits often pass over or through ridges, and thus transgress natural drainage divides. Although some ditches were built by prehistoric Papuans for crop irrigation, particularly in the Baliem Valley, most were constructed during the past century for municipal water supplies or to provide drainage in urban and industrial areas. At higher elevations, such systems are generally associated with mining developments, such as the Grasberg mine above Timika, while at middle elevations they include a wide array of local water supplies ranging from rudimentary split bamboo flumes to joined plastic pipes many kilometers long.
The environmental character and biota of ditches and flumes differs with their location and degree of use, but in upland Papua they often contain high-quality water comparable to midreach stream water. In general, a lack of shelter and slack water results in low faunal diversity, with the most prominent biotic elements being certain aquatic mollusks, Diptera, Heteroptera, Odonata, and occasionally atyid shrimps, with fishes generally scarce. In lowland areas, particularly in or near larger towns, effluent ditches are commonly constructed to remove water from small reservoirs, agricultural sites, and use facilities. Water quality in such effluent ditches is moderate to low, and the macrofauna, when present, consists mainly of introduced fishes and hardy invertebrates.
Lentic Ecosystems
Lentic ecosystems are defined as standing or still waters, generally in definite basins. They may be divided into two types, lacustrine and palustrine, depending on the type of basin they occupy.
LACUSTRINE SYSTEMS (LAKES AND PONDS)
Lacustrine ecosystems are standing waters occupying definite basins with discrete shorelines, and have predominantly open water with depth generally exceeding 2 m. Such ecosystems are numerous in Papua, and vary greatly in size, from small montane ponds to large lowland lakes, and even flooded World War II bomb craters.
Natural Lakes and Ponds
This ecosystem class comprises natural freshwater lacustrine ecosystems (Figures 5.5.8–5.5.12) with salinities less than 0.5 o/oo, including limnocrenes (pond-like springs with subterranean limnetic water sources). Although relatively uncommon in the tropical Pacific as a whole, such ecosystems are well represented in Papua due to its young, rugged topography and extensive karst exposures. These factors have combined to create many areas with blind or poorly integrated drainages, particularly in the Lengguru Fold Belt of the Vogelkop region (Figure 5.5.10), and to a smaller extent in the strike valleys along the crest of the central mountains (Figure 5.5.9). The lake systems of Papua are extensive, and each individual lake is distinctive in terms of its location, environmental features, and native biota (for a list of major lakes in Papua and their endemic biota (see Table 5.5.1). The natural biotas of such systems in the lowlands include many fishes, especially melanotaeniids and gudgeons, as well as Zygoptera in the families Lestidae (Lestes) and Coenagrionidae (Agriocnemis, Ischnura) and Heteroptera in the families Gerridae (Limnogonus), Mesoveliidae (Mesovelia), and Veliidae (Microvelia), in addition to a diverse waterfowl assemblage (Erftemeijer and Allen, 1989). These systems are frequently degraded by introduction of exotic food fishes, particularly carp and tilapia (see further discussion later in this chapter). By contrast, alpine lakes, such as Lake Andersen near the Grasberg mine (Figure 5.5.9), support a limited and specialized insect biota of Diptera in the family Chironomidae, and Coleoptera in the family Dytiscidae (tribe Bidessini), and also represent important habitats for native waterfowl such as Salvadori’s Teal.
Figure 5.5.8. High alpine lakes, such as these formed at the base of melting glaciers near the summit of Mt Jaya, are numerous along the crest of the highest mountains in western New Guinea, but relatively poor in aquatic biota.
Photo: D. A. Polhemus.
Figure 5.5.9. Lake Andersen, near the Grasberg mine, is typical of alpine lakes formed in strike valleys amid the tilted limestone layers of the central mountains of Papua. Note the series of lakes that occupy basins of progressively lower elevation along the westward strike of the valley. Such ecosystems contain specialized suites of aquatic insects such as Coleoptera and Trichoptera, and also serve as important habitat for waterfowl such as Salvadori’s Teal. They are devoid of native fishes.
Photo: D. A. Polhemus.
Figure 5.5.10. Lake Laamora in the Bird’s Neck region of Papua, shown here in the dry season, is trapped amid a parallel series of limestone anticlines upthrust in the Miocene, and has a seasonally fluctuating water
