The estuary region and the characteristics of the partition

Scientists have noted the differences between the three categories of  water (river, sea and estuary) with regard to the degree salinity or freshness, and they have found that most creatures that livee in the sea, river and estuary die if they are taken out of theirown environment. That which lives in the river cannot live sea or estuary, and so on.

  Then they classfied the three environments (river, sea and estuary ) on the basis of the creatures that live in them, and they foundbthat the estuari region is regraded as a barrier that is exclusive to most of the creature that live in it, which cannot live anywhere but in an aquatic environment that has a certain leved  of salinity or freshness, and they die if  they go out of the estuary region.

  In addition to that, the estuary region is regarded as a barrier that excludes most of the creatures that live in the sea and river, because these creatures will die if thgey enter this region, which is also due to the water pressure. The wonder is that the Qur' an described the estuary region  in these terms and said "a complete partition". We can understand the world Hijr  (partition) here in the light of modern studies which show that living creatures in the estuary region live in a narrow space and are preventedfrom leaving that space.
  
  The estuary region is also described as being forbidden to othe living creatures which cannot enter it.


So the estuary region, according to the Qur'anic description, is A hijr that is specific to the creatures that live in it "forbidden" to the creatures that live outside of it

1. The estuary area is regarded as an area that is exclusive to the creatures that inhabit it and as an area that excludes creatures that live inthe river and sea. This what Allah, the Exalted, descrbies in Sr, Al-Furqan: "and He has set a barrier and a complete partition between them".
2. The second barrier is that which separates salty seas; it does not have that characteristic of preventing creatures from leaving or entering. This is what is referred to in Sr, Al-Rahman where Allah, Most High, s

   بَيْنَهُمَا بَرْزَخٌۭ لَّا يَبْغِيَانِ ﴿۰٢)  فَبِأَىِّ ءَالَآءِ رَبِّكُمَا تُكَذِّبَانِ ﴿١٢﴾ يَخْرُجُ مِنْهُمَا ٱللُّؤْلُؤُ وَٱلْمَرْجَانُ﴿٢٢)                                  

     Between them is a barrier which none nof them can transgress. Them which of the Blessings of your Lordwill you both (Jinn and Man) deny? Out of them both come out pearl and coral " ( sr. Al-Rahman ; 55:20-22)

    The barrier is not described as " barrier and a complete partition"; hence, we find that most creatures can move between the two seas with complete ease. That is becase the difference in salinity levels is not so severe as to prevent them moving from one marine environment to another.

   So the human mind stand amazed by miraculous wording of the Qur'an and this amazing system that Allah has created to protect the masses of water from spoiling each other's characteristic wen they meet.

                    


  وَقُلِ ٱلْحَمْدُ لِلَّهِ سَيُرِيكُمْ ءَايَٰتِهِۦ فَتَعْرِفُونَهَا ۚ وَمَا رَبُّكَ بِغَٰفِلٍ عَمَّا تَعْمَلُونَ ﴿٣٩﴾  

And say [(O Muhammad S A W  to these polytheisists and pagans]: All the praises and thangs be to Allah. He will show you His Aayat (Sins in yourselves, and in the universe or punishments), and you shall recognize them". Sr, Al-Naml; 27:29)


Scienific references

The Encyclopaedia Britanica says:

• River estuaries are places where the river meets the sea,and they may also be described as place where the ratio o salt in sea water is reduced as it mixes with freshwater.
• From a biological point of view, estuaries are more poductive than rivers and seas, because estuaries have a special and distinct kind of water cycle which retains plant nutrients and encaurages primary production. Because freshwater is lighter then salt water, this leads to the formation of a sparate layer that floats on the surfaceof the estuary.
• On the boundary between the fresh and salt water, there is a certain level  of mixing that is caused by the flow of freshwater above the salt water and because of the ebb and flow of the tide. Any additional mixing could occur from time to time because of high winds and internal waves that are generated along the interface between the fresh and salt water.

The Encyclopaedia mentions elsewhere: 
Salitnity in the oceans is fixed but it fluctuates along the coastwhere salt water meets freshwater at the mouths of streams and rivers. This brackish water forms a barrier that separates sea creatures from river creatures.

The miraculous aspect

    The miraculous  aspect in these Qur' nic Verses is that they point to the precence of barrier between salty seas that alow slow mixing, whereby the water that moves from one sea to another loses its characteristics and acuires the characteristics of the sea it enters. They also indicate that seas and rivers meet and mix , although there is a barrier that prevents complete mixing between them. This something that was discovered by oceanographers in the twentieth century about estuaries where rives meet the sea, and the marine barriers betwen two different seas. And Allah knows best and is Most Wise.