Ecology of Indonesian Papua Part Two. Andrew J. Marshall
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a seasonally fluctuating water level. It supports an endemic rainbowfish species.
Photo: G. Allen.
Artificial Reservoirs
Reservoirs consist of lacustrine waters occupying artificial basins or human-made impoundments. In contrast to other parts of the world, Papua lacks large-scale reservoirs created by high dams, although many smaller artificial basins and impoundments built for various purposes are scattered throughout the province, intermixed in a few areas along the north coast with small artificial basins created by warfare, in the form of water-filled bomb craters. In addition, the construction of logging roads often inadvertently creates unplanned reservoirs of varying size and duration due to the obstruction of streams by culverts and other temporary crossings.
The environmental quality of such reservoirs and their resulting biotic assemblages vary with reservoir type. Primary storage reservoirs, built primarily for agricultural and domestic water supplies, frequently lie on or near source streams in remote upland sites, and have relatively stable surface levels and good water quality. As such, they often support submerged and floating water flora, which in turn provides excellent habitat for aquatic insects and mollusks. Distributional reservoirs, by contrast, lie mainly on agricultural lands or in populated areas, and are used mostly for temporary water storage and redistribution. As a result, they have fluctuating surface levels and moderate to poor water quality, with their waters often turbid. Accidental reservoirs created by warfare or road construction vary widely in environmental quality and may exhibit any of the above characteristics.
Figure 5.5.11. Lake Sentani, near Jayapura, is formed in a basin lying between the accreted terrane of the Cyclops Mountains to the north (right side of picture), and the foothills of the Foja Mountains to the south (left side of picture). It contains at least three species of endemic fishes.
Photo: D. A. Polhemus.
Although they are artificial ecosystems in terms of basin origin and structure, such ecosystems are often colonized by dispersive native lowland aquatic insect species, particularly wide-ranging Anisoptera in the families Libellulidae (Pantala, Diplacodes) and Aeschnidae (Anax), and Heteroptera in the families Belostomatidae (Appasus), Nepidae (Ranatra), Notonectidae (Anisops), Veliidae (Microvelia), and Mesoveliidae (Mesovelia). They may harbor rainbowfishes and a few other native fish species, but are also frequently stocked with livebearers and rivulines (for mosquito control) as well as food fishes such as tilapia.
Saline Lakes
Although present as shoreline features or closed lagoons on other islands in the region with seasonally drier climates, particularly Timor and the Lesser Sunda Islands, saline lakes have not been documented in Papua. The shores of such lakes, which have waters with salinities exceeding 0.5 o/oo (and in some cases exceeding 100 o/oo), typically support a limited but extremely distinctive halophytic (salt-adapted) biota, particularly among certain insect groups such as Diptera in the family Ephydridae and Heteroptera in the family Saldidae (Pentacora, Micracanthia, Saldula).
PALUSTRINE SYSTEMS
Palustrine ecosystems, more commonly referred to as ‘‘wetlands,’’ comprise various types of swamps and marshes with lentic waters less than 2 m deep (usually <1 m), occupying irregular or poorly-defined basins (Figures 5.5.12–5.5.15). This category encompasses a broad array of individual ecosystems that tend to form a continuum, and creating an unambiguous classification to accommodate the full range of variation involved has proven problematic, but as a general rule forested wetlands are considered to be swamps, while open, non-forested wetlands are classified as marshes.
Figure 5.5.12. The vast wetlands bordering the Mamberamo River in the Meervlakte basin form a complex mosaic of lotic and lentic ecosystems, the latter including both lacustrine and palustrine components.
Photo: D. A. Polhemus.
Palustrine ecosystems include wetlands at both high and low elevations, each with several types. Elevated wetlands, located in remote areas, are primarily natural systems in which native biota dominates, good examples being the marshes that are frequently encountered in the upland valleys of the central mountain ranges. Low elevation wetlands have in most parts of the Asia-Pacific region been severely modified by humans (IUCN, 1991), but in Papua they retain a largely natural character (Figure 5.5.13), due to a general absence of rice cultivation and consequent channelization. This situation is changing, however, in the Merauke and Jayapura regions, where physical alteration of wetland structure and introduction of invasive fishes is rapidly transforming such ecosystems.
Upland Bogs
Upland bogs comprise small bodies of acidic open water on flat, elevated topography at elevations generally above 2,000 m in areas of high persistent rainfall (> 300 cm year). The soil substratum beneath such bogs tends to be primarily organic, producing clear, cool (< 16° C) waters that are very low in dissolved minerals (conductivity <30 µmhos), stained yellow to brownish with humic solutes, and acidic (pH < 5.5). Such bogs are widely distributed in the Papuan uplands, and are distinguished by their strongly acidic water chemistry and impoverished invertebrate faunas, which include aquatic Diptera in the families Ephydridae and Dolichopodidae. Due to their elevation, these bogs uniformly lack fishes.
Upland Swamps and Marshes
Upland marshes are perennial to seasonally intermittent, non-forested wetlands in upland areas (100–1,200 m) of moderate to high rainfall, but with better drainage than boglands. Their waters are clear and sometimes yellowish, with low to moderate dissolved mineral content (conductivity 30–80 µmhos), and circumneutral (pH 5.5–7.5). Emergent aquatic plants (sedges and grasses) are often abundant, including Drosera, Gentiana, Utricularia, Brachyposium, Carex, and Scirpus. Their fauna is similar to that of bogs described above, but more abundant and diverse.
Figure 5.5.13. The diversity of juxtaposed lotic and lentic aquatic ecosystems in lowland New Guinea is well illustrated in this satellite image from the Kikori River basin of Papua New Guinea. Aquatic ecosystems visible in this image include lowland rivers and their tributary creeks, mixohaline mangrove swamps, freshwater swamps, and freshwater marshes.
Photo: D. A. Polhemus.
Upland swamps are perennial to seasonally intermittent forested wetlands in upland areas (100–1,200 m) of moderate to high rainfall. Their waters are non-acidic, with characteristics similar to those of upland marshes. By comparison to marshes, however, their fauna is more diverse and often endemic, including a few fishes (often gudgeons of the genus Mogurnda), specialized Odonata in the family Coenagrionidae (Ischnura), and Heteroptera in the family Veliidae (Microvelia, Neusterensifer).
Overall, upland marshes and swamps appear to be more productive than bogs, and support a greater faunal diversity. Such ecosystems tend to be localized and of relatively limited extent, forming either in natural depressions, or in areas where streams are impounded by either natural barriers or by the construction of road crossings.
Freshwater Lowland Swamps and Marshes
These ecosystems comprise naturally occurring, shallow, standing, perennial limnetic waters in lowland areas at elevations < 100 m, which may occupy either definite or indistinct basins not immediately adjacent to the coastline, with emergent flora predominant. They are maintained by either stream inflow, or by exposure of the natural water table. Water quality in such systems may be variable, but salinity is always < 0.5 o/oo (conductivity 100–300 µmhos), with nearly neutral pH values of 6.0–7.5.
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