『Abstract
Living plants, which acquire significant amounts of K primarily
from weathered silicate materials, may be considered as an intermediate
storage for part of K that is ultimately of the origin of silicate
mineral weathering. Part of this plant K is transferred to streams
and rivers, as dead vegetation on the ground surface and within
the soil beneath the surface becomes decomposed and leached by
surface and ground waters, with the remaining K being recycled
to new growth of plants. The plant K transferred to rivers was
never included in any previous budget model that assessed the
sources and pathways of K in global river. A popularly current
view claims that nearly 87% of the total K in global river water
comes from weathered silicate source, relative to 5% from evaporite
deposits, 1% from atmospheric salt cycling, and 7% from fertilizers.
In fact, some fraction of this silicate-material derived K in
global river should belong to plant source K derived from leaching
of dead vegetation on the surface and in soils as being a source
of K in global river was assessed by using a mass-balance equation
that expresses the K/Rb weight ratio of global river in terms
of fractional contributions of K from various sources to global
river water and the K/Rb ratios of the contributing sources.
Considering a wide range of values for the K/Rb ratio of each
source of K in global river water, calculations have shown that
of the proposed 87% silicate-derived K in global river water,
nearly 70 to 30% can be attributed to leaching of dead vegetation
on the surface and in soils by surface and ground waters, whereas
the remaining 17 to 57% can be assigned to leaching of the weathered
silicate materials by surface and ground waters. A more realistic
estimate can be based on taking into account the average crustal
silicate K/Rb ratio of about 250-300. By this measure, the K derived
from leaching of decayed plant by surface and ground waters is
at least as important as the K derived from leaching of weathered
silicate materials by surface and ground waters (4344% each),
and may be even more important than the K derived from leaching
of the weathered silicate materials (70-72% for the plant source
K, in contrast to 15-17% for the silicate source K), as a control
of the dissolved K in global river water. We have also estimated
that nearly 97-98% of K released from dead vegetation on the surface
and in the soils is cycled back each year to newly growth plants.
Keywords: Potassium; Plant; River; Silicate』
1. Introduction
2. Theoretical considerations
3. K/Rb ratio of world river water
4. K/Rb ratios of various sources of k in global river water
4.1. Ranges of K/Rb ratios of marine evaporites as a source of
K in global river water
4.2. Ranges of K/Rb ratios of the atmospheric salt cycling K
in global river water
4.3. Ranges of K/Rb ratios of fertilizers as a source of K in
global river water
4.4. Ranges of K/Rb ratios of solutions following dissolution
of silicate materials
4.5. K/Rb ratios of land plants at a global scale
5. In the absence of any plant input, how important is leaching
of weathered silicate materials by water as a source of K?
6. Can plant materials, as they go through decay and leaching
by surface and ground waters, be a major source of the dissolved
K in global river water?
7. Annual recycling of K by plants
8. Conclusions
Acknowledgments
References