[1끊어읽기] TOEFL Reading : Seagrasses 3  

3 paragraph

Since most seagrass systems are depositional environments, 

they eventually accumulate 

organic material 

that leads to the creation 

of fine-grained sediments 

with a much higher organic content 

than that of the surrounding unvegetated areas.

This accumulation, in turn, reduces 

the water movement and the oxygen supply.

The high rate of metabolism

(the processing of energy for survival)

of the microorganisms

in the sediment 

causes sediments

to be anaerobic

(without oxygen)

below the first few millimeters.

According to ecologist J.W. Kenworthy, 

anaerobic processes 

of the microorganisms

in the sediment 

are an important mechanism 

for regenerating 

and recycling nutrients and carbon, 

ensuring the high rates of productivity

---that is, the amount of organic material produced---

that are measured 

in those beds.  

In contrast

to other productivity in the ocean, 

which is confined to various species of algae 

and bacteria dependent on nutrient concentrations

in the water column,

seagrasses are rooted plants

that absorb nutrients

from the sediment or substrate. 

They are, therefore,

capable of recycling nutrients

into the ecosystem 

that would otherwise be trapped 

in the bottom 

and rendered unavailable.