Summary
In his introduction to Lamentations, Daniel Grossberg has this to say about authorship:
Ancient tradition, reflected in the Talmud, the Septuagint, and the Vulgate, ascribes authorship of the book to Jeremiah, the leading prophet at the time of the destruction, whose book bears a resemblance to the language of Lamentations. Modern scholars do not accept the notion of Jeremian authorship (as they do not accept the ancient ascription of other biblical books to biblical figures). They ascribe each chapter to a different anonymous author, whose identity is impossible to ascertain.1
While five separate authors would fit the idea Lamentations was originally five separate psalms complied into one, I believe all of the literary devices used create a unified structure which is best explained as the work of a single writer: Jeremiah.
The Four Primary Acrostics
Daniel Grossberg describes the basic poetic structure:
The first four chapters are structured as alphabetic acrostics, with each verse beginning with a letter of the Hebrew alphabet in sequence. Ch 3 is a triple acrostic. (The sequence in chs 2-4 reverses the order of the letters "pe" and "ayin"; this reflects an alternative order of the alphabet found on inscriptions from Izbet Sartah and Kuntillet Ajrud.)...The verses in chs 1 and 2 are relatively long, with three "poetic lines" in each. Ch 3 is composed of short verses, three for each letter of the alphabet, with each verse falling into two parts. Ch 4 returns to the use of longer verses, but with two "lines" in each instead of three. Ch 5, although not an acrostic, has twenty-two single-line stanzas. (Twenty-two is the number of letters in the alphabet, so the last poem has the same number of verses as Chs 1, 2, and 4.)2
As the alphabetic sequence of Pe-Ayin is considered older, this abecedarium could be used to date chapters 2, 3, and 4 to earlier writers; it also creates three primary divisions within the work:
Of course a writer like Jeremiah would likely be aware of the earlier sequence and simply chosen to use both. For example, since Chapter 1 describes the condition of Jerusalem and Judah after the destruction, it is chronologically "out of order" from Chapter 2. In other words, the use of the historical abecedarium is patterned after the chronology used to describe the events:
Chapter 1 - Describes the aftermath of the destruction
Uses the later abecedary
Chapter 2 - Describes events which occur before Chapter 1
Uses the earlier abecedary
Chapters 4 and 5 exhibit a similar treatment except the order is reversed:
Chapter 4 - Describes events which occur before Chapter 5
Uses the earlier abecedary
Chapter 5 - Describes the aftermath of the destruction
No acrostic
The three acrostics with the earlier Pe-Ayin alphabet sequence are used in those chapters which describe earlier events than those in Chapters 1 and 5; this suggests a single writer whose purpose(s) in using different acrostics included what could be called a "real-time" element to the structure. Rather than construct a chronically correct sequence, the writer chose to begin in the final devastation and reflect on the past before ending by returning to the present. Their use of different alphabetic sequences is a way of authentication: they are lamenting what they experienced.
The Secondary Acrostic
Chapter 5 lacks a full 22 letter acrostic, yet as Homer Heater Jr, notes, there is a four-letter acrostic:
verses 19-20 are themselves a mini-acrostic used to express the highest praise for Yahweh [YHVH] in the book followed by a tentative, but hopeful cry for help
Yahweh [YHVH] is sovereign!
A — Thou, O LORD, dost rule for ever;
K — Thy throne is from generation to generation.
But O LORD do not abandon us!!
L — Why dost thou forget us forever;
Z(sic) — Why dost Thou forsake us so long?3
Heater uses letters in English to identify the acrostic. Here it is in Hebrew:
19a Alef: אַתָּה יְהוָה לְעֹולָם תֵּשֵׁב, "You YHVH forever remain."
19b Kaf: כִּסְאֲךָ לְדֹר וָדֹֽור, "Your throne is from generation to generation."
20a Lamed: לָמָּה לָנֶצַח תִּשְׁכָּחֵנוּ "Why forever do you forget us?"
20b Tav: תַּֽעַזְבֵנוּ לְאֹרֶךְ יָמִֽים, "And forsake us for so long a time?"
These particular letters and their arrangement are symbolic of the entire alphabet:
A: First letter of the alphabet
B: Eleventh letter - the middle of the first half of the alphabet
B': Twelfth letter - the middle of the second half of the alphabet
A': Last letter of the alphabet
The Ending Pe's
As noted in enegue's answer, a Pe is placed at the end of the four alphabetic acrostics:
1:22 תבא כל־רעתם לפניך ועולל למו כאשר עוללת לי על כל־פשעי כי־רבות אנחתי ולבי דוי׃ פ
2:22 תקרא כיום מועד מגורי מסביב ולא היה ביום אף־יהוה פליט ושריד אשר־טפחתי ורביתי איבי כלם׃ פ
3:22 תרדף באף ותשמידם מתחת שמי יהוה׃ פ
4:22 תם־עונך בת־ציון לא יוסיף להגלותך פקד עונך בת־אדום גלה על־חטאתיך׃ פ
This device signals the end of an an acrostic and, since each acrostic is a different poem lamenting different events (and in different genders - see below), it also signals the end of that lament.
Chapter 5, also has a Pe; it is placed at the end of verse 18:
5:18 על הר־ציון ששמם שועלים הלכו־בו׃ פ
Chapter 5 comes to a much different ending than the other chapters. So in terms of the overall content of the chapter, the Pe functions to mark the end of the fifth Lament:
5:1-18 The fifth lament ended at v.18 as marked by an ending Pe.
5:19-20 But you, O LORD, reign forever; your throne endures to all generations
Why do you forget us forever, why do you forsake us for so many days?
5:21-22 Restore us to yourself, O LORD, that we may be restored! Renew our days as of old
unless you have utterly rejected us, and you remain exceedingly angry with us.
Finally, since verse 5:18 begins with the letter Ayin, the Ayin-Pe sequence is used in the final line of the final lament. "Lamentations" as such effectively ends at 5:18. The Book closes with praise to YHVH and a request for restoration. Here is the complete outline the writer used:
The Chiastic Arrangement
The acrostics of Chapters 1, 2, and 4, are written such that only the first letter of the first line uses the acrostic letter. Chapter 3 is a triple acrostic because all three lines begin with the acrostic letter. This creates a chiastic arrangement for the three pe-ayin chapters. This element is preserved when a different abecedary is used in Chapter 1 and a different acrostic is used in Chapter 5:
Chiastic Arrangement of Acrostics and events
A: Chapter 1 - Later alphabetic sequence - laments the destruction
B: Chapter 2 - Early alphabetic sequence - describes the destruction
X: Chapter 3 - Early sequence used in triple acrostic
B': Chapter 4 - Early alphabetic sequence - describes the destruction
A': Chapter 5 - 4-letter acrostic - laments the destruction
The final arrangement indicates Chapter 3 is the central theme of the Book. In fact, it is here where the first mention of hope is introduced:
The turning point is in the third poem, chap. 3, which presents a change from despair to hope. Verses 22-39 present the conception that God's mercies have not ended (v. 22) and the sufferer must await God's salvation (v. 26). Verse 31 determines that God has not cast off Israel forever; the situation will change. These verses are the turning point, leading from the despair of chaps. 1-2 to hope in chaps. 4-5. Lamentations 3, which is rightly considered by many scholars to be the crux of the book, deals with the theological perspective of the destruction.4
With this in view, here is a brief summary of the five chapters:5
1: Jerusalem and Judah after the destruction. Only despair; no request for deliverance
The LORD has done this. Ends with a plea for the LORD to deal with the enemies
as He has dealt with Jerusalem and Judah.
2: Goes back in time to describe the events of destruction. Again it is the LORD who
did this. No expression of hope, comfort, or deliverance; there is only despair.
3: There is hope. The steadfast love of the LORD never changes; His mercies are new
every morning. The LORD will not cast off Israel forever. Repent and return to the LORD.
4: A repetition of chapter 2 but with an expression of hope and a focus on the enemy not
the LORD who has done this. Ends with a request for the enemy to be punished.
5: Returns to reflection on the destruction yet begins with a plea to the LORD.
Ends with praise and a request to the LORD.
Number of Lines and Gender
Unlike some acrostic Psalms, each in Lamentations is "complete" with 22 letters. Therefore each chapter, including the one without an acrostic has 22 stanzas. The number of lines appears to be an integral element to the structure. Chapters 1, 2, and 3 have 66 lines, three per stanza. Chapter 4 has 44 lines, two per stanza. Chapter 5 has 22 lines, one per stanza.
As noted in the question, the primary gender of a chapter varies. Chapters 1 and 2 are feminine; chapter 3 is masculine; chapters 4 and 5 are a "collective" witness. Here is a summary of all the literary structural features for all chapters:
The varied use of gender, like the triple acrostic, highlights Chapter 3.
While Chapter 4 is shorter than Chapters 1, 2, and 3, it combines with Chapter 5 to total 66 lines. This suggests Chapters 4 and 5 were written with this element in mind. That is to say, just as a "collective" gender would include both male and female, the 2 collective gender chapters combine to 66 lines. This "2 in 1" relationship implied in the gender of chapters 4 and 5, parallels in the number of lines and the number of acrostic letters in the entire work:
Chapter 1 2 3 4 5 Total
Lines: 66 66 66 44 22 264
Letters: 22 22 66 22 0 132
Two Groups of Seventy
Within the entire work, there are five acrostics, three composed of 22 lines which start with a acrostic letter, one with 66 lines, and one with 4 lines:
Chapter: 1 2 3 4 5
Acrostic Letter lines: 22 22 66 22 4
Central theme & ending -- -- 66 -- 4 [70 acrostic lines]
Supporting themes & ending 22 22 -- 22 4 [70 acrostic lines]
The 4 line acrostic in Chapter 5 when considered with the 66 lines of the triple acrostic, total 70. Similarly when considered with the supporting chapters, the total is 70. Thus, the 4 letter acrostic at the end of the work can be taken as a fitting ending to both the central message of Chapter 3 and the combined supporting messages of Chapters 1, 2, and 4. This is another "2 in 1" aspect which can be found in the entire work.
Seventy is particularly significant at this moment in history because it is the number of years Jeremiah twice prophesied the exile would last:
This whole land shall become a ruin and a waste, and these nations shall serve the king of Babylon seventy years. Then after seventy years are completed, I will punish the king of Babylon and that nation, the land of the Chaldeans, for their iniquity, declares the LORD, making the land an everlasting waste. (Jeremiah 25:11-12) [ESV]
“For thus says the LORD: When seventy years are completed for Babylon, I will visit you, and I will fulfill to you my promise and bring you back to this place. (Jeremiah 29:10)
Moreover, the two 70-year prophecies in Jeremiah summarize two themes in Lamentations, the enemy will suffer like Zion (1:22, 4:22) and there is still hope for God's people (3:22, 5:21)
Therefore, Lamentations not only reflects a variety of structural elements integrated into a whole, the whole may be seen as producing two allusions to Jeremiah's 70-year prophesies. The most reasonable explanation is Lamentations is the work of a single person writing soon after the destruction of Jerusalem; that person at a minimum would be contemporary to Jeremiah.
If this is so the lone masculine poem is likely Jeremiah's personal lament:
I am the man who has seen affliction... (Lamentations 3:1)
The triple acrostic corresponds to the three-fold nature of Jeremiah's suffering:
Brought about by the LORD who chose him
Brought about by his own people who mistreated him
Brought about by by the enemies of Zion. Jeremiah was not spared from the collective experience of all Jerusalem and Judah
Similarly, if the writer is Jeremiah, three elements of time would apply: Jeremiah prophesied before the destruction; he experienced events and now he is lamenting. This is another explanation for the triple acrostic.
Conclusion
It is unlikely an editor could find 5 different psalms each with all the proper features which could then be complied into a single Book. Rather, the most likely explanation for the unity of the structural elements is they are the work of a single writer. Since the structure also indicates a writer who was contemporary to the events, the most likely person is Jeremiah, as every ancient source holds.
Note:
1. Daniel Grossberg, The Jewish Study Bible, Edited by Adele Berlin and Marc Zvi Brettler, Oxford University Press, 2004, p. 1589
2. Ibid., p. 1588
3. Homer Heater Jr., Lamentations
4. Elie Assis, The Alphabetic Acrostic in the Book of Lamentations, The Catholic Bible Quarterly, Vol. 69 No. 4 (October 2007), p. 722
5. Ibid., pp.710-725
