Acid Sulfate Soil

Acid sulfate soils are naturally occurring soils, sediments or organic substrates (e.g. peat) that are formed under waterlogged conditions.

These soils contain iron sulfide minerals (predominantly as the mineral pyrite) or their oxidation products. In an undisturbed state below the water table, acid sulfate soils are benign.

However, if the soils are drained, excavated or exposed to air by a lowering of the water table, the sulfides react with oxygen to form sulfuric acid.

Release of this sulfuric acid from the soil can in turn release iron, aluminium, and other heavy metals (particularly arsenic) within the soil.

Once mobilized in this way, the acid and metals can create a variety of adverse impacts : killing vegetation, seeping into and acidifying groundwater and surface water bodies, killing fish and other aquatic organisms, and degrading concrete and steel structures to the point of failure.

Chemical reaction

When drained, pyrite- (FeS2) containing soils (also called cat-clays) may become extremely acidic (pH < 4) due to the oxidation of pyrite into sulfuric acid (H₂SO₄)..

2FeS₂ + 9O₂ + 4H₂O 8H⁺ + 4SO₄^2- + 2Fe(OH)₃

Fe(OH)₃, iron(III) hydroxide (orange), precipitates as a solid, insoluble mineral by which the alkalinity component is immobilized, while the acidity remains active in the sulfuric acid.

The process of acidification is accompanied by the formation of high amounts of aluminium (Al³⁺, released from clay minerals under influence of the acidity), which are harmful to vegetation.

Other products of the chemical reaction are:

1. Hydrogen sulfide (H₂S), a smelly gas

2. Sulfur (S), a yellow solid

3. Iron(II) sulfide (FeS), a black/gray/blue solid

4. Hematite (Fe₂O₃), a red solid

5. Goethite (FeO.OH), a brown mineral

6. Schwertmannite, a brown mineral

7. Iron sulfate compounds (e.g. jarosite)

8. H-Clay (hydrogen clay, with a large fraction of adsorbed H⁺ ions, a stable mineral, but poor in nutrients)

Wild Ficus of Seremban

 Ficus subpisocarpa

Ficus subpisocarpa ( called 笔管榕 in China and 雀榕 in Taiwan ) is a species of small deciduous tree native to Japan, China, Taiwan and southeast Asia to the Moluccas.  The figs are ramiflorous, that is the fruit grow on the branches.

Two subspecies are recognized  : pubipoda and  subpisocarpa . 

Ants predominantly of the genus Crematogaster have been recorded living in stem cavities. Ficus subpisocarpa is pollinated by Platyscapa ishiiana (Agaonidae).

Ficus hispida

Ficus hispida ( 对叶榕 ) is a small but well distributed species of tropical fig tree. It occurs in many parts of Asia and as far south east as Australia.   An unusual feature is the figs which hang on long stems.

Two subspecies are recognized  : rubra and  badistrigosa . 

In Australia the fruit are eaten by cassowaries and double-eyed fig parrots. Phayre's leaf monkey feeds on the leaves as do the larvae of the moth Melanocercops ficuvorella. The fig wasp Apocrypta bakeri has F. hispida as its host, where it parasitizes the other fig wasp Ceratosolen solmsi.

 Ficus grossularioides

Two varieties are recognized  : stenoloba and  kingii .

Young shoots are eaten raw; decoctions of leaves are used to treat kidney complaints.  Latex is used against scorpion bites.

Bouea oppositifolia - kundang

Synonyms
Bouea angustifolia Bl.
Bouea brandisiana Kurz
Bouea burmanica Griff.
Bouea burmanica var. kurzii Lecomte
Bouea burmanica var. microphylla (Griff) Engl.
Bouea burmanica var. roxburghii Lecomte
Bouea diversifolia Miq.
Bouea gandaria Blume
Bouea microphylla Griff.
Bouea myrsinoides Bl.
Cambessedea oppositifolia (Roxb.) Wight & Arn. ex Voigt
Haplospondias brandisiana (Kurz) Kosterm.
Manga acida Noronha
Mangifera oppositifolia Roxb.
Mangifera oppositifolia var. microphylla (Griff.) Merr.
Mangifera oppositifolia var. roxburghii (Pierre) Tard.
Matania laotica Gagnep.

Uses
Fruits are edible and are sometimes made into preserve when in a half ripe state. The durable, hard timber is used for various purposes.

Distribution
Southern China, Indochina, Myanmar, Thailand, Andaman Islands, Malay Peninsula, Sumatra, Java; Borneo.

Local names
Borneo: asam djanar, bandjar, kedjauw lepang, tampusu, ramania pipit, umpas.
Indonesia: Asam djanar; Bandjar; Kedjauw lepang; Kundang rumania; Ramania hutan; Ramania pipit; Rengas; Tampusu; Tolok burung; Umpas.
Malay Peninsula: gemia, kemiinia, kimdang, kiidang rumenia, merapoh rumenia, poko rummiyah, rambainyia, ramimia, romaniah, rumboi-nigor, rumenia, rumia.
Sumatra: kaju-rusun, kunangan, raman burung, raman padi, raman utan, rieden daun, gandaria, raman, iiris, iirisan.