Geographical environment of marsh of Nanren Lake or the so-called “Nanren Lake Swamp” is referring to the water area of Nanren Mountain area (includes independent Nanren Lake, Yilan Lake, and central water area); the central water area is commonly known as Nanren Lake or Nanrenhu (南仁湖).
“Nanren Lake Swamp” is the largest hydrostatic lake ecosystem in the water area of Nanren Mountain. The Mount Nanren Ecological Reserve Area (南仁山生態保護區) which is located at the northeast corner of the national park is affiliated to Manzhou Township of Pingtung County.
When driving along Taiwan County Highway 200 of Pingtung to the control station of Mount Nanren Ecological Reserve Area (about 135 meters above sea level) and then walking from west to east along the Nanshan Road Nature Footpath (about 3.1 kilometers), you would reach Nanren Lake (about 325 meters above sea level); the whole round trip takes about 3.5 hours when walking.
Mount Nanren Ecological Reserve Area. Image Source.
Topographically, the area where “Nanren Lake Swamp” is located is a mountainous hilly area that extends southward from the central mountain range.
Geologically, the surface rock is mainly composed of clay, sand, and gravel; it is differentiated from the Micocene rock formation of the Cenozoic era.
It is the oldest rock formation of Hengchun Peninsula.
Loess is the most conspicuous among the exposed soil around Nanren Lake.
Hydrology of “Nanren Lake Swamp”
“Nanren Lake Swamp” is the largest freshwater body in the water area of Nanren Mountain, and it belongs to the coastal catchment area of Jiupeng.
The lake was not formed naturally. In the early days, Nanren Lake was originally only a few small swamps, which were formed by the collection of natural rainwater at the hollows of the low mountain group.
Since the late Qing Dynasty, farmers had planted paddy here, and they built ponds for irrigation by intercepting water in the mountains according to the terrain of mountain.
Due to the inconvenience of transportation to the outside of the area, and because of the poor loess which resulted in unsatisfactory yield of paddy, in recent years, huge number of farmers had moved out. The abandoned paddy fields had been converted to buffalo pasture.
In the seventy-first year of the Republic of China, the outlet of the “Red Soil River” near the northwest corner was blocked by artificial embankments, and the accumulated water could not be vented, thus forming a water area of about 150 hectares at present.
. Ecologically, marsh of Nanren Lake formed a freshwater ecosystem of its own. Because of the peculiarity of the location environment, the average person often regarded Nanren Lake and its surrounding environment as an ecosystem of water area at Nanren Mountain.
According to the habitat environment of the organism, the water body of marsh of Nanren Lake itself can be divided into three types of water bodies: the central lake-type still-water area, the lakeside swamp-type still-water area, and the river-type flowing-water area of which it connects to branch streams (e.g., “Ba Lu River” and “Red Soil River”). There are obvious differences in term of biota which inhabited different still-water areas and flowing-water areas.
The area and water level of water body in marsh of Nanren Lake show seasonal changes, and they are mainly affected by monsoons and rainfall of dry and wet season. More on Kenting Climate here.
For example, the lake near the longhouse of the village was originally narrow; during the dry season, the water level would drop significantly, and more than half of the area of the lake would be exposed to the air, forming a phenomenon that the lake surface was divided into two.
During the wet season, due to the rise of the water level, the lake surface which was divided into two was once again connected.
Usually, the water level of Nanren Lake is about 0.5-2.0 meters, while the water depth in the lake shore area is mostly about 0.3-0.5 meters. It thereby forms shallow water areas, paddy field areas, hay slopes, and other diverse environment at the area towards the direction of land.
Water quality of “Nanren Lake Swamp”
The salinity of the water body of “Nanren Lake Swamp” is about 0.2g, of which it belongs to the water area of pure freshwater.
This water area is located at the Mount Nanren Ecological Reserve Area, and other than the influences of agriculture and pasture on water area in early day, the water body is not contaminated by public pollution.
Survey data in recent years had pointed out that the pH of the lake water was mostly less than the neutrality (pH 7), and the water quality had the phenomenon of partial acidity.
Apart from the fact that the soil at the bottom of the lake does not provide sufficient alkalinity to the lake water, the cause of this type of acidification is also related to the decomposition of advantageous plant clusters (mostly refers to annual herbaceous plants such as bareet grass and others) after death which releases lot of organic acids.
If you are interested read more about plant life in Kenting National Park, you can read this article.
In addition, the excretion of waterbirds and cattle nearby flows into water body of still-water type, thus reducing its pH.
The dissolved oxygen content of “Nanren Lake Swamp” shows little variance (about 5-10 mg/L) throughout the year, of which this is enough to meet the survival of aquatic organisms. In recent year, the nutrient salt concentration of phosphate in the water of lake was high, and the content of chlorophyll a was also high, indicating that the content of phytoplankton in the water was huge.
These also showed high productivity of water. It is mainly because nutrient salts are the basic elements for the growth of phytoplankton, so usually the higher the content, the more conducive environment for the reproduction of aquatic plants, and this further increases the chlorophyll content of the water body. In term of classification of water body, regardless of phosphoroate or chlorophyll a content, the water body of Nanren Lake can be classified as optimized lake.
Nanren Mountain is inhabited by plenty of birds, buffaloes, and other animals. Their excretion flows into the lake, and the nutrient salts are continuously imported into the lake through natural soil infiltration water, thereby contributing to the possible optimal and sustained cultivation of Nanren Lake in future.
Taiwanese Macaques in the area
In term of ecosystem, Nanren Lake is a highly productive water area. Due to the proximity to the tropical monsoon forest area, the local temperature is high all year round with the water temperature of Nanren Lake is on average more than 20 °C, and this increases the rate of decomposition of organic matter (decaying plants and waste of water birds, buffalo, as well as fish).
Water temperature of Nanren Lake is on average more than 20 °C, and this increases the rate of decomposition of organic matter (decaying plants and waste of water birds, buffalo, as well as fish).
This affects the pH and oxygen content of water, and the dissolved oxygen of the water body of “Nanren Lake Swamp” is as much as or more than 5 mg/L, of which this directly affects the ability of aquatic organisms to reproduce.
Ecology of “Nanren Lake Swamp” the pattern of water area of Nanren Lake is deeply affected by monsoon and rainfall of wet and dry seasons. In the central water area of Nanren Lake, the water level of about 0.5-2 meters deep is maintained over the years; the water body on the shore of the lake changes according to the amount of dry and wet seasonal rainfall, thus forming shallow water areas, paddy field area, hay slopes, etc. This causes aquatic, hygrophytic (or wet plant), xerophytic, and other plants to be grown, resulting in a diversity in Nanren Lake. It is also home to a variety of aquatic invertebrate animals, fish, and other aquatic organisms.
In addition, around Nanren Lake, apart from a short grass wetland, protected natural broad-leaved forest at the edge of the grassland still can be seen; many invertebrates, amphibians, reptiles, birds, and other wild animals inhabit in the forest.
Plant Ecodiversity of Nanren Lake
There are about 27 species of aquatic plants in the water area of Nanren Lake.
According to the growth state of angiospermae in water bodies, it can be divided into three categories.
Angiospermae of plants such as Spirogyra sp., Najas minor, Riccia fluitans, and Rotala wallichii are all immersed in water to reproduce, and these plants are known as “submerged aquatic plants” (Submergent macrophytes); windflowers, Nymphaea tetragona, and floating fern are completely floated on the surface of the water, thus they are known as “free-floating aquatic plants” (Floating macrophytes).
Najas Minor
Bareet grass, Taiwan spikerush, rush-like bulrush, old world arrow-head, and other plants containing roots which are buried in the mud and the angiospermae which grow above the water are classified as “emergent aquatic plants” (Emerged macrophytes).
As in the whole area, the emergent bareet grass is the most widely distributed and conspicuous plant in the swampy lake area of Nanren Mountain.
Taiwan Spikerush
The wet plants of the clustered area of swampy lake at Nanren Mountain mostly grow at wet places such as areas around the water area of Nanren Lake as well as inside abandoned paddy field.
The area where wet vegetation is distributed is characterized by plenty of plant type and weeds which evenly occupy the space in between.
Due to the flowing water and trampling of grazing cattle, the land of these areas is gradually divided into many small pieces, and this is especially shown in the place originally for field stems, of which it is easier to form piles of haystack.
The ecosystems of the succession from these haystacks have become the habitat of goose, ducks, and other waterbirds in the areas of Nanren Mountain; the area next to the haystacks are also the breeding grounds for small invertebrates such as field snails, etc
Plants that widely cover the fields, roadsides, hilltop, and mountain slope at the area of Nanren Mountain are xerophytic grassland plant.
In this area, because of grazing cattle and other human activities, the original forest vegetation is hummed and trampled before turning into a low, flat, and felty grass slope. In the community of typical pastoral grassland, the composition is dominated by Chrysopogon aciculatus, and there are also Miscanthus spp. in between. Murainagrass, Eragrostis unioloides, Digitaria fauriei, other associated ferns, Ixeris oldhami Kitamura, etc.
Ecology of animal from swampy lake Water area of marsh in Nanren Lake is inhabited by a variety of freshwater animals which include aquatic insects, fish, and other animals.
Among the ecological systems, it is the most eye-catching, and it is easy to explain its freshwater ecological relationship. Aquatic insects are an important link in the food chain of ecosystem of water area of Nanren Lake.
Common representative species include dragonflies, Odonata spp., Gerridae, Sphaerodema rustica, Laccotrephes pfeiferiae, Ranatra fabricius, pine borer, Dytiscidae, etc. Their forms are very different. Each of them also has their own feeding habits and habitat ecological location.
In terms of fish, the existing species in the central water area of “Nanren Lake Swamp” include Tilapia and goldfish; the existing species in the swampy shallow water include Rajsh Cichlasoma, pond loach, Hong Kong catfish, mosquitofish (Gambusia affinis), rice eel, etc.
It is worth worrying that at present, there are already invasion of exotic species such as mosquitofish and Tilapia in the “Nanren Lake swamp”. In particular, the Tilapia grows rapidly, and it has strong ability to reproduce
Apart from having a strong territorial nature, it is also good at digging holes at the bottom of the pond as a nest, and it preys on the juveniles and eggs of other type of fish.
Nowadays, Tilapia has become an absolute dominant species in the water area of Nanren Lake, of which this phenomenon will threaten the survival of other fish and other organisms, while at the same time destroy the ecological balance of the water area.
Marsh of Nanren Lake contains rich vitality and wild interest of nature. In a tour to the lakeside, you can see the green grass by the lake and the island group that is flying freely.
When climbing up the hill of Nanren Lake, looking up at the blue sky and white clouds as well as looking down at the shadows of the cattle egret and the buffalo walking on the same path, in addition to the lingering color of water due to the projection of mountain light on the lake surface.
People will be inevitably moved by these scenes. From this, it is not difficult for us to obtain insight from the story of Nanren Lake, about its formation and succession as well as mysterious ecological relationship between a freshwater lake and the surrounding environment.